What Causes Pain In Joints And Radiating Pain From Shoulder To Armpits?

My name is Laura I have been having alot of joint pain to the point that I can not move my left arm without the help of my right arm. This pain is located from the very top of the (L) shoulder to underneath the arm pit area. What could cause this much pain when getting up in the mornings or from just taking a nap? This pain almost feel like I ve lay on the top of my shoulder the wrong way. It hurts even to make a sudden move. And has been like this for several months it just seems like its getting worst. I haven t lifted anything heavy.