In Dec. Of 2014 While Reclined In Bed--elbow Set On

In Dec. of 2014 while reclined in bed--elbow set on mattress-- I reached back to answer my cell which was also on mattress and felt searing, tearing, grinding pain rip down upper, outer left arm. Pain took my breath away. With months pain continues and stiffness set in. Cannot raise my arm now. Cannot extend arm to shave armpit. Just won't move there but also because painfull. Have had Xray and MRI which show no shoulder problem no arthritis in joint, slight inflammation present. Dr. highlighted this on MRI report mailed to me that's it. Pain horrible but not constant. Now have big knot half way down arm which HURTS when touched. Any ideas?????