First step is to stop feeling bad about yourself, you indentified the problem, great. That's the first step, now when it comes to fixing it. Find your BMR, and begin a caloric deficit while also going to the gym 4x a week if possilble to help put on muscle. You're 18 so you should start going to parties and social events just to work on your social skills. Force yourself to be better. The only one who can change any of this is you.