Exercising bad or good?

ok so im 15. 130 pounds and 5'7. I work out and am very active. Im athletic and lately i been notcing i been losing my fat. Idk if thats good. Im losing my . idk if that means im getting it toned so i gotta build up my muscle or that im losing my in a bad way. I dont have much of a anymore and im wondering how i can get a bigger . is this normal? exercising and losing my butt fat. i think it's getting more toned but my butts practiclly gone and i have a bony butt now. :(