Heya and welcome.
Generally at your age its a good idea to make sure you eat regularly, and not overly huge meals. Exercise is great idea, but try to make it interesting (like a sport or something).
Ideally you should read the threads in the Newcomer area, they have a ton of information!
As far as sports go, try faster sports that may involve running (soccer, hockey etc usually team sports) or others that may involve all your body muscles and take a good few hours a week training (Cheerleading, Gymnastics, Dance, weights, wrestling etc)