What Causes Severe Pain In Left Shoulder Radiating From Neck To Left Arm?

I have severe pain in my left shoulder blade, it radiates to my neck and down my left arm. No tingling or numbness. I had an injury to this area a couple years ago and lately have experienced these symptoms after waking up. This is the 3rd episode over the past several months but it s not going away this time. Muscle relaxers, anti-inflammatories and pain meds help but do not completely alleviate all symptoms. What are the possible diagnosis?