Why do people consider me heavy?

I am a 15 year old girl and weigh 53.5 kg (118Lbs) and am 167cm tall "5'6" I started puberty at around age ten and that is when i started noticing my rapid weight gain. I was fairly discontent with it. I was taller than the other girls i was about 5'2 and weighed 100 pounds (45kg) whilst the other girls all weighed around 77Lbs. They told me I was heavy and probably needed to loose 5kg (11Lbs) I tried to but couldnt succeed. So at age 13 I had my real weight problem. I stood on the scale once and weighed a whopping 121Lbs I cried. I dieted and managed to loose 4.5Lbs and have stayed the same since then. My weight however can fluctuate. Right now though at age 15 some girls are taller than me and i am averagish. The guys look down on me like a midget. I used to be taller than most. And many girls are heavier than me.