What Causes Tightness And Tenderness In Upper Arm Followed By Bruising?

About two weeks ago I awoke with a tightness and tenderness in the upper arm just below the armpit. The discomfort continued to spread down the arm to my wrist accompanied by discoloration (bruising?). The muscles do not appear to be affected. I am unable to extend my arm without discomfort, or raise my arm above my head without considerable pain. This past week I began getting red and purple spots on the lower forearm. They have disappeared in some locations with a day or two, but the last one to appear have been present for two days. My armpit is very tender to bathe or apply deodorant. I have not fallen or experienced any other trauma.

Help.