What Could Be The Cause Of Back And Shoulder Muscular Pain?

I started with pain on the back of my right shoulder and it moved down to the front of my shoulder. Pain goes away for one day then comes back the very next day & it hurts to lift my arm! I got massaged & felt like a little bubble on between my armpit & front shoulder but now it feels like my whole muscle is aching. What can I do to make the pain go away. I was just laying down about a week & a half ago wen I felt like a knot on my shoulder