Good answer demiguise!
I have the same problem, and am seeing a chiropractor on a regular basis to try to alleviate some of my symptoms. You may consider trying to sleep on your back, or on your other side. My husband makes fun of me, because I have to sleep turned away from him in order for my arm to not hurt. He tries not to take it personally!
Mine has gotten so bad that my fingers go numb when I'm fixing my hair, or putting on makeup.
Try to see a doc...a chiropractor...and he can begin to teach you things about posture, etc that can help you.
I'm getting shoulder pains in my left shoulder and a pressure feeling in my left bicep and sometimes feeling dizzy- I almost slipped a disc in my back last summer and from what I'm reading in alot of these posts it is probably from that back injury