body issues... help

am i fat? be honest!!! i’m so worried about my weight and how big i am. whenever i try to talk about it with my friends they just tell me “everybody’s different” and “you’ll grow into your body later on in life” but i’m already like 15 and i keep gaining and losing weight. right now i’m 131 pounds and i feel like i just keep gaining. should i do more exercise or eat healthier? please give tips!