I'm a 16 year old female, and a healthy vegetarian. The other day I went to the gym after not having gone for over two weeks. While working out I hurt my left shoulder so I stopped and went home. The pain went away quickly. But tonight I was just sitting in my room when my left shoulder suddenly started hurting a really sharp pain that hurts more when I move it. I want to know if this is a serious problem? and what it might be as well as what I can do about it.