Im 15 and 1/2 i weigh 187 pounds, i'm not huge but im not happy with how i look i'm 5'6"?

my weight is distributed pretty evenly and i like to keep up with fashion im considered a trend setter at school. i really want to loose weight, i've done it before. when i loose weigh i drop 20 pounds almost instantly after that it gets challengling, because i drop weight so easily the last time i lost weight my friends thought i was anorexic and got very concerned i lost a few gained a few and one almost shoved ribs into my mouth. any advice on the best way to loose the extra weight and how much i should loose.