I exercise everyday and eat healthy, why am I gaining weight?

I am 125 pounds and 13. I have skinny arms and my legs are huge. I have almost like a tire around my lower abdominal and I have stretch marks on my inner thighs. I think I have a muffin top. I hate wearing swim suits because my stomach looks big because it kind of hangs over the bottom of my swim suit. I am self conscious of my stretch marks and I go to the gym every day. I eat reasonably healthy and I workout everyday. I'm not gaining muscle. It's almost as though I'm getting fatter! I'm really confused! I need diet help! I don't want to go on a crazy diet, just speed up my metabolism. I used to be anorexic, but I have gotten over that and have been eating normally for like a year. I really need some advice cause I'd love to loose my stomach fat and hip fat and inner thigh fat by August. A big goal, I know. But I'm willing to do the work. Help me please?!?!?