What is the key to my losing weight?

I found one website, it had pictures and asked me questions as i scrolled down. In my mind I'm thinking "No" but all the questions were about one thing: overeating. Aren't there more factors then that? I don't eat that much each day, and being a middle schooler, I can't "snack throughout the day" and have three meals. My exercise everyday is swimming slow laps for an hour since juneI(since I read how many calories you lose, I plan on going faster :), but I've only lost 2.3 pounds! I don't have a working scale at home, and I went to the Boston Children's Hospital and had it checked there during my visit (I had a heart echo done, two weeks before a kidney ultrasound). What gives? I also see a nutritionist if that matters.... But why haven't I lost more? It's been two months!