I need help with my distrusting thighs !!?

so im 15 and i weigh 140 and im 5'7 im not sure if thats healthy or not but every time i go to workout my thighs get muscular and they get bigger and bigger not small so i feel like im getting fat when really its all muscle i want it to be thin not muscle. im a size 11 and sometimes a 9 and i want to be a size 3. everyone else who works out gets thinner i get more muscular and i hate it. Please help someone. and also i havent worked out in a while but i always have like these wierd fat clumps on the back of my thighs and i think its ceelulite and i need to get rid of it please help