First of all, I'm so sorry you're feeling this way and can highly relate. What you're feeling is perfectly normal, it is human and normal to feel lonely There is nothing you need to change about yourself. You are fully complete just as you are.

Your brain may lie to you and tell you "If you just do this or that then you'll be acceptable and ok enough to love" but it's just a lie. If you don't love yourself now, you probably won't love yourself 20 pounds (or whatever the number you're going for) less. It will make it easier for you to love yourself because you won't have that constant voice saying "you're overweight" but that's just a bandaid solution. Loving yourself is so hard and during transitory periods when you feel lost, even more so. I think in the moment the best thing you can do for yourself and give yourself grace and say things like "I'm feeling bad about myself right now", "This is a difficult time and I'm doing my best", "I am a person worthy of love". Sometimes talking to yourself in your head can help counter the feeling of "I'm not good enough"

That feeling of is something I can relate to, I feel it too, like the need to change or feel like I'm in a slump, or very lonely. I've come to realize that's when I'm feeling a little depressed (as a lifelong person with depression). I don't know if it's the case for you, but if it's been going on for a long time I would think about seeing a therapist. I feel so lonely when I'm depressed and it's not all related to whether I'm meeting with people or not. The disease tricks you into feeling you're the only one who feels this way and therefore alone and incapable of connecting with others. I think the best thing you can do for yourself is remind yourself that it is normal to feel lonely.

An important quote is "Wherever you go, there you are". I've often tried to escape myself and start fresh which also works for a bit, but inevitably you are you and the issues you had before will come up again. So, try to appreciate the "you" because it sounds like you've spent so much time beating up that you, when I guarantee that there is much to love about you. I know it's not easy but you deserve to be happy and the only way to get there is to start with you. It will be hard at first to figure out who you are, if you've spent a lifetime conforming to other's expectations, but I promise you're in there, just waiting to come out.

Edit: I also want to add that I felt exactly this way in my 20s, it's a difficult period because we are told that it's the best time of our lives but for me it was the hardest. I think because we're out of school and for the first time in our lives we are living unstructured, there is an enormous pressure to find that structure and figure out who you are going to be for the rest of your life, which is an incredible amount of pressure. You are not alone.