What Causes Soreness In Arm, Armpit And Elbow?

I have a pinching sensation which has become increasingly more sore, and localized to a 2.5-3.0 inch area in the medial upper arm, beginningalmost at the armpit almost to the anterior elbow. It sems to be right under the bicept. I do not remember any injury, fall, etc. to the area. any ideas? should I see a doctor? It is not debilitating, but pain increases when I stretch the arm straight. and above my head. Thanks. YYYY@YYYY