I have been having sharp pains now for a week under my collar bone on my left side. It is painful to the touch on the bone itself at the base of the neck near the sternum. There is no bruising, and it doesn't appear that anything is disloacted, however I cannot straighten my shoulders back to stand up straight without considerable pain. Extending my left arm straight back also causes pain. I cannot think of any specific trauma that could have caused this problem. I do aerobic activity and weight lifting 5 times per week. The pain seems to be getting worse everyday, and it is interferring with everyday activities. Should I see a doctor right away, or wait awhile longer? What could be causing this problem?