It doesn't sound like you're really eating a lot of calories. Maybe try eating a larger variety of foods, including more fiber. You'll be less hungry and you won't be gaining any weight. Honestly though, I was still growing at your age, I gained some too around that time, it could be you're getting taller and adding a little more to your frame. I ended up gaining a little too much after puberty (I ate junk for every meal), about 45 pounds in just a few years. I probably should have only gained 20-25. This was from middle school to high school. You seem like you're eating better than the average teen, so that's great. Here are some meal ideas:
Breakfast: Thomas' Light Multi-grain English Muffin toasted with peanut butter (the Light EM has 8g of fiber, it's good too), an english muffin toasted and in between a crispy Morningstar Farms sausage patty (egg and cheese are optional), Kashi Autumn Wheat cereal (lots of fiber), oatmeal, Buckwheat pancakes, or any cereal with vitamins and minerals.
Snacks: Pita Chips with Hummus, Celery with hummus, dry cereal, fruit, nuts (I love cashews, esp mixed with dried cranberries), sunflower seeds (in shell and salted, they're delicious, salty without too much sodium, and take a while to eat).
Lunch/Dinner: Amy's Meals (Veggie Loaf has 8g of fiber, so does the Black Bean Tamale Verde, both are delicious), whole grain pasta with eggplant parmesan, grilled portobello burger, homemade pizza.
It's early, that's all I can come up with right now. The idea to is eat satisfying meals and avoid the kitchen when you're bored. That's my problem, I eat out of boredom. I had homemade Eggplant parmesan a few nights ago and it was SOOOO good (even as leftovers) and I honestly wasn't hungry the rest of the night after I had it. I used this recipe:http://www.recipezaar.com/Eggplant-P...atchers-237164
I made some modifications, you can see my review on the right side.Pretty easy to make. I served it with Ronzoni Healthy Harvest Whole Grain Pasta. I loved it so much I'm tempted to make it again today
Good luck, I'm always here if you need me!