I feel so sad, am i doing something wrong? help?

i feel like i dont fit in with my friends or at school, i dont really like myself i sometimes feel like im wasting life. i want to change and be a nice and better person. I feel self contious even around friends im a junior in highschool and im a cheerleader i feel like ive never really been happy and im wondering id im doing something wrong? i wnat to live a different life, i dont mean to sound negative do you have any advice for me?