You exercise, so that's a plus. You can always bump it up a notch. If it's jogging around the block, or doing push-ups in your room, or whatever. Y
You should ask your parents to be supportive regarding the junk food, but if they won't be, you'll just have to be strong and resist it. As far as fast food goes, go to the website(s) of the restaurant(s) that your parents frequent, and find out what the healthiest alternatives are.... Wendy's has wonderful salads, Taco Bell has the "Fresco" options. Hardee's has the Low-Carb Thick Burger. Choose wisely, and fast food can be good for you.... Remember Jared from the Subway Commercials? Maybe your parents would be willing to go to Subway more often, or at least pick up a sub for you while they're stopping somewhere else. Even at McDonald's you can get a grilled chicken sandwich, hold the mayo. I'm sure you can talk your parents into buying healthy cereal, and at least a quart of skim milk. So just ignore the doughnuts, be strong and eat a healthy breakfast.
If nothing else, google the number of calories that Micheal Phelps eats in a day.... You CAN make healthier choices and excercise your way out of it!