There is a weight problemo among an adolescent here...?

How do I put this... I'm 15 year old sophomore and I am in dire need of advice. When I was in 8th grade, my diet at school was mainly pizza and at home, the stereotypical "black meat preference", pork chops (fried). I don't like fried foods because: it's gross, it's cooked in excessive fats, and the greasy residue left over on your plate and on your mouth is just absolutely disgusting. Anyway, after having that fixed diet for 2 years so far, I have weighed myself and estimated my gross weight gain to be approximately 15 lbs. My metabolism in the 7th grade was at an all time high. Due to the lack of running for 3 years (well, immoderate running) I've slowed down drastically. I still have my energy, but my speed and stamina attributes have depleted... I've also been eating more than my metabolism's capability in digestion. Do I still have the metabolic speed? If so, how do I lose this somewhat small amount of belly flab (the fat mainly shrouds around my naval)? Exercise and dieting is obvious, but it seems to have become harder to lose this weight. I'm figuring it's from aging, but who knows? That's why I'm on here. Please give informative and, if you must, somewhat comical answers, por favor. Gracias. :D