Hi there dear. Here's my personal advice for you. It is what has worked for me, so maybe you can learn something here!
First, good for you for realizing the need to get in shape!
At your age, staying active is equally important to eating right. Start paying attention to your meals. Make sure half your plate is veggies (salad, broccoli, carrots, whatever you like!), then the other half is split between a lean protein (steak, chicken, fish, etc) and a healthy starch (baked potato, corn). Also, a lot of snacks out there have tons of starchs that could really ruin an exercise plan if you're not careful. Watch your carbs-- enjoy 1 carb meal a day. So if you know you're having pasta for dinner (I hope it's whole wheat!), avoid bagels or sandwiches for your other meals. Also, keep up the water! I know it seems like it's not helping, but just keep it up. It's so much better than sugary sodas and juices!
Also, take some vitamins. A young, growing man needs all the vitamins and minerals he can get to sustain his hungry body! I take a multivitamin like Centrum and a fiber supplement.
Changing your eating habits can be difficult and takes quite a bit of effort, but once you get used to it, it'll be a piece of cake!
Keep staying active. Try walking around the neighborhood, playing your Rock Band drums, and biking, at least once a day. This, combined with the healthy eating, should help you.
Good luck and feel free to contact me with further questions!