How can a 15 year old girl like me lose weight?

Okay so I used to be thin and weighed 102lbs and now I'm 125lbs. That is 23 pounds I've gained! Before puberty I was thin and very active. I'm still active but trying to lose weight. My mom said I'm just filling out and getting curves and it's normal. Well I'm going to look womanly but I dont wanna be fat. I'm 5'2 in a half. I can't even fit into ny favorite jeans anymore so I had to get new ones because of my hips and fat butt. Girls at school said I have a Kim Kardashian ass and boys stare at it and said I have a sexy ass. I need to lose weight. Other girls said I'm so lucky to be thick and guys like thick girls. I'm not thick am I?