I am a 15 year old girl and I weight about 140. Very often throught some days my left shoulder starts to hurt. If I was to rate the pain on a scale of ten, throught the day it ranges from a 3 to a 7. This pain is on and off and sometimes it just doesn't hurt for the day. Oh, i dont do any sports or anything, im lazy. And when it hurts, i could me sitting down, standing up, walking, anything. What could this be, it is really starting to bother me?