Pain in shoulder blade and arm and can't sit. What is the connection?

1 week ago I suddenly got a sharp pain in my right shoulder blade and the outside of my right arm.  My ring finger, pinky and right forearm are weak.  My reflexes are ok. I cannot sit or walk for more than a few seconds without severe pain. The pain can be reduced if I bend my head slightly down and increased if I bend it back.  Two years ago I had similar symptoms which were attributed to a 4mm tear in my rotary cuff and a dislocated right head long shoulder tendon.  If the problem is my neck or my shoulder, why can't I sit without pain?  Which nerve could be impinged and how to treat it?   I have been in bed for a week, have difficulty sleeping and am looking for help.   Any advice is appreciated.