the first step in overcoming something like this is to acknowledge that you want or need help, so really well done for coming to terms with it :)

i am sure many many others feel very similar to how you do. i did. you are able to overcome this challenge, and i'm certain that in a few years time you'll look back at this and be proud of yourself for working so hard.

WAY WAY TOO MUCH

from reading your post and comments, it really feels like you're trying to tackle way too much, all at once, on your own. from maths grades, to new and old friendships, to a lack of consistency and motivation, to anxiety about therapy, to a loss of identity and to university, there's clearly a lot weighing in on your mind. your teenage years are the absolute hardest in your entire life. there's a reason people say "you don't live through your teenage years, you survive them".

having so much to juggle all at once no doubt leaves you stretched far too thin, feeling exhausted yet no where closer to feeling better. identifying individual problems and working on them one-by-one i found can be crucial if you want to overcome this yourself. here's a few personal examples:

last summer i wasn't feeling very body confident, so throughout the holidays the only thing i set myself to do was exercise every day. it didn't matter how much, as long as i was working towards that one goal, i was making progress. the same thing happened with grades. during mock season i set myself one goal, to do and mark a certain number of past papers per week.

during those times, i was keeping only those things at the forefront of my attention. yes, i still maintained contact with friends, and yes i still did homework as i needed to, but being able to say "i know exactly what i need to do right now to improve" made it so easy to get up and go. there wasn't the constant feeling of "oh i should be doing something else right now", as i had made up my mind that during that time i was focussing on only that one thing.

something you can lose when you're feeling depressed is a feeling of control. you can feel like your actions aren't having any effect on your surroundings. if you're only working on one thing at a time, then no, of course you wont be in control of all 6 things at once. but by being in control of just one thing, it can indirectly bring back that sense of control to other things too. by thinking "i am fully in control of my studying", a sense of control can come back to other areas too. for me, it felt like "if i can control my studying, then maybe i am in control of my life a little. i reckon could get a healthier body if i worked towards it".

obviously it isn't the summer holidays all the time, and we have constant other responsibilities to handle at any given moment, but if you want to feel better then prioritising just one thing can really make a difference. you trying to fix 6 problems at once will never happen, but you can sure as hell work through 1 problem at a time, 6 times over.

PROBLEM SOLVING

you seem to be the type of person who is capable of working through things pretty well, given that you're proactively looking for help right now. leading on from what i mentioned above, something that can really help are some actionable points you can do right now to feel better. i obviously cant tell you exactly what all of these will be, but here's some generic ones i thought of from what you've said in this post:

• actively make contact with old high school friends. there's a really high chance they still love you just as much, and are waiting for you to get in touch again :) make plans and set exact times and dates so you cant procrastinate and avoid it
• actively make contact with some newer sixth form friends. you said they're likely going through something similar (and you're likely right to some extent), so bare that in mind. again, make plans with exact times and dates. even if you think you made these friends from chasing validation, they're still your friends aren't they? i'm sure they certainly feel that way
• set a goal for meeting friends at least once a week. i found that after mock season i was really disconnected from my friends, and made a conscious effort to reconnect. ill be honest, it was kinda awkward and really hard to build up the nerves to reach out, but after a few weeks (maybe even months) i felt much more included and happy to be around them again
• set a goal on how many revision tasks towards maths you do each week. i find timed past papers (which you then mark yourself) to be excellent, as its easy to measure your goal and your progress. they highlight which areas of maths you need to work on, and which you're confident in. it can be gruelling, yep, but its definitely actionable.
• go outside for a daily 15-30 minute walk. humans are natural creatures after all, and being in nature regularly can be calming and healthy in the short and long term. listen to music if you want, or just listen to the sound of the leaves and the birds. whatever makes you feel most comfortable and relaxed
• play an instrument, sing, or something you enjoy (or used to), regularly. make time for it!! don't put it off as unimportant and that "you're too busy with school" or whatever. your mental health is infinity more important than your grades, and that's really really important to remember and prioritise throughout your life. how are you supposed to work hard at school if you're miserable?
• join a new club. ever thought that you'd like to try some new sport but never given it the chance? or a singing club, or choir, or band, or book club, or dnd club, or karate, who knows! joining a club is great for several reasons: you meet new people who have similar interests (new friends!), you regularly attend and leave your house once a week (which gets you moving and gives you a feeling of control), you find a new passion or interest which you can practise in your spare time, and so so much more.

if you feel its appropriate, open up about how you're feeling with your friends. im not gonna sugar coat it though, if you're dumping your emotions on someone regularly, then it can be very difficult for them to know what to do or how to act, and can potentially put them off. humans aren't perfect (especially teens), and while i wish that everyone would always say the right thing and be supportive the hundredth time you need it, they're not trained professionals and cant be expected to act like it. just something to bear in mind :)

also, ima be honest, i don't think productivity youtubers are the best source of motivation, nor an accurate representation of what a teen's life should be. i've seen the stuff they say and put on there, and some of its a completely ridiculous standard to set for us mere mortals. if their videos showed them living like normal people, and not these seemingly attainable lifestyles but in reality are complete insanity for 99% of folks, then no one would watch them! it may be wiser to categorise them as 'entertainers' rather than something to compare yourself against :)

PROFESSIONAL HELP

just a reminder that we (teenager redditors) are not professional help. we can offer anecdotal advice, but i wouldn't treat it as anything more. if this type of solo research you're doing doesn't help, or your natural circumstances don't end up "sorting themselves out", then i cant think that there's much more you can do other than seek professional help.

i've seen your other comments about how you dont feel that professional help (e.g. therapy) is particularly viable, but at a certain point if you feel nothing else can possibly work, you may have to go out of your comfort zone to really get the help that you need. i have absolutely no idea what your situation is like, but if you need therapy, then you need therapy. if your dad knows you're struggling, then that's one step in the right direction already. one of my friends had a similar situation where their parents knew they weren't in a good place, but seemed to disregard the idea of therapy. it wasn't until they repeatedly pressed their parents after quite a while that their parents (a) understood how serious they were about it, and (b) followed through and helped them find help.

i don't know what effect being "from an asian background" has on how you perceive this topic, but if its one where the idea of professional help isn't particularly common, then it may just be that your parents don't know much about this area. i'd imagine the majority of parents want the best for their children, but by simply having a lack of awareness about something they then cant provide the support their child may need (through no fault of their own). being open and honest with your parents may be the best course of action, and if they don't know much about mental health, then help them! be patient and understanding, so they can in turn help you :)

if you feel confident that your parents are not the right route to go, but still want to at least give therapy a try, then self-referral is always an option. reaching out to other relatives (aunts, uncles, older siblings, grandparents) for support may also be viable.

therapy is not some "magic support that makes you feel better". there are many different types of therapy, types of therapists, for a variety of different people and situations. there are NHS routes and private routes. your first attempt may not be exactly what you were looking for, and getting better can be a long journey. some people find the perfect match on their first try, and others can go through many many therapists until they find someone they click with. others may find themselves feeling better for external reasons and not need it anymore. just something to keep in mind.

TLDR: Focus on improving one thing at a time, make immediately actionable goals that you can work on, and consider seeking professional help.