You probably don't weigh enough for someone 5'6"; I am 5'6" and my low weight that I weighed for 10+ years at your age was 127 and many thought me too thin; though I did not have an eating disorder, was anxious instead. I'd go to my doctor and get a physical, talk with them and see what they think. I wouldn't pay a whole lot of attention to what your friends think; if you don't know and it's about "you", how can they have a clue?