About 3 months ago I started experiencing pain in my arm. The pain pretty much right in the middle of where my shoulder and elbow are. It's very localized and if I swat at something it causes excruciating pain. It also hurts at night and I have to sleep with my arm at my side. I don't know if it's muscle, bone or what. I didn't do anything that I recall to start the pain but it hasn't subsided and seems to be getting worse. Any ideas on what it is?