I NEED TO LOSE WEIGHT!!!!?

Hi I'm 14 and totally overweight. I eat healthy and drink water and diet pepsi. I need help to lose weight because I just got into High School and I know if I lost weight I'd look beautiful. I have tried south beach, weight watchers, atkins, guaranteed diet. I have done so many diets and the thing is iots not like I'm anorexic I'm 5foot 11 inches and 275 pounds but I hide it well. Please help if you have any ideas.