Possibly pinched nerve in upper left shoulder area. Radiates up neck and down left arm. Very painfully. Only relief when I lay flat on back.

I PAIN. You need ct scan/mri of cervical spine to see disc, vertebra, nerve compression, osteoarthritis, fasciae and muscles. The appropriate management depends on correct diagnosis. Please see your doctor. Thanks.
Radiculopathy. You should see a doctor. It sounds like you have a radiculopathy, in which a cervical nerve is being compressed, possible by a cervical disc.