i agree with those who workout. taking drugs may help but i dont know about long term =/ i don't really condone the use of drugs to help lift self-esteem. i know plenty of people who are super depressed who take drugs to feel happy then come back even more depressed to the point of killing themselves or harming those around them. this is not for all people but that is my experience.
definitely do some sort of cardio. running and swimming can help very much. possibly eating more healthier can help you feel good about yourself too. and maybe even getting the right amount of sleep. first you should at least take care of yourself and your body and once that's going, you'll probably feel a lot better about the other things around you.
maybe school isn't for you? i do believe education is important but if you really feel as though school isn't enough, maybe traveling and learning about different cultures and opening your eyes to the world that's not the US (i dont know where you're from) can help with insightfulness and possibly motivation.
well in the past, excercise (mostly running) has helped me, but it seems as if any peace of mind I get from excercising is pretty temporary.
i will definitely try eating healthier.
as for travelling, i don't have any money, i'm underage, and noone in my family is well off.
i might go volunteering at an animal shelter or something, but honestly i am an extremely negative person and im not sure if it will help