Is there any way I could speed up my metabolism?

I've heard there are certain foods that are supposed to speed up your metabolism. I try to exercise every day, aside from walking all over school campus. When I do exercise, I walk, do 40 reps of 5 different types of sit ups/crunches, 50 jumping jacks, and I do 20 reps of 5 different types of punches with 5 pound weights. I try my hardest to eat and drink healthy... See, I drink tons of water every day, meaning I urinate several times a day, even several times an hour sometimes. However, I do eat a lot. But whenever I eat, I lose it in the toilet sometimes as little as a few minutes later. I'm not bulimic, but I think I have irritable bowel syndrome or something. So, sadly I'm a little bit chunkier than I want to be. I'm a 14 year old female, about 5'1", and around 115 pounds. I don't want to lose weight, just inches. Is there anyway I could speed up my metabolism to lose those inches? Any helpful answers will be greatly appreciated. :)