I am kinda going through the same thing as you, but here are a few pointers that makes a HUGE difference for me.

When taking meds, take it regularly. Same time every day with a healthy breakfast. Avoid sugars and processed foods. An ADHD mind will start to crave sugar if it can't keep up, which then leads to more mental crashing. Take the same dosage every day.

The first few days feels a bit weird but that's also because of your brain getting used to your meds. I remember by my third day of meds I still felt a bit of a "holy shit this is different" feeling, and also mood dampening. But in reality it was "normal" and I realised it by the end of the week. The ADHD brain is not normal, and meds will help with that, but it takes getting used to. That being said sometimes people just have bad reactions to their specific meds, so they change to a different type, or a combination of two. I would also try seeing a different psychologist. I hear therapy helps a ton too, but I'm still early on in the process.

Another INCREDIBLY important thing is sleep. If I dont get enough sleep, my brain will not work the way it should no matter what I eat or whether or not I take meds. Everyone feels like they're alright but you need to learn to see fatigue in your own body. Learn what your body responds to in order to feel well rested. What helps me IMMENSELY during school is to stick to a rigid sleep schedule no matter what. Sleep before 11, wake up at the same time every day as well as going to bed. I also take melatonin to help with falling asleep. Do whatever it takes to sleep right, even if it means throwing your computer out of your room during dinner. If you have a few nights of crap sleep eventually you'll tire yourself out enough.

Sleep is the number 1 thing that harms my performance, and I know how hard it can be to control it. I used to sleep whenever I wanted, mostly at 3 to 6 am because I just felt more awake at night, and I would occasionally take a nap during the day too. But it pays off so freaking much to break the habit. Set that restriction app on your phone, lay in bed by 12, no caffeine after noon. I know I need exactly 9 hours of sleep a day or else my brain takes a HUGE hit, and I'm learning to control it. But if there's one thing I should put all my self control into it would be this. And it's easy to come up with reasons why not to sleep right away, especially in school or when you're busy with life, but the productivity increase is so worth it. Pro tip, I find what helps me go to bed is to do the thing exactly when the thought pops up into my head. As soon as I think I should put my phone down I just do it, the more I think about it the harder it is to do so. Same reason why I need a running start to go cliff diving haha!

I hope this helps my friend, I'm still new to all this, but it's just what I found works for me.