The problem with working out every single day for two hours or more is that you're not giving your body a chance to rest. Rest days are when your body gets stronger; even pro athletes have rest days!
What happens is you start to break your body down instead of building it up. You risk burnout, injury and more. Being young isn't a good excuse to to abuse your body... you have to take care of it, because running it into the ground now will make it more difficult to recover lately.
BECAUSE you're young, you need to be just as careful.
Oh, and to answer your original question, here's the expert answer that explains why you've gained weight: www.sparkpeople.com/community/ask_the_expe