61yo male, pain in upper left arm for past 6mo, limited range of motion. could this be pinched nerve or due to long-standing diabetes? what is tx?

Pinched nerve: Shoulder and/or upper arm pain can be caused by an irriated shoulder (bursitis/tendonitis) or a pinched nerve in the neck. If turning your head in the direction of pain causes the pain to shoot to your shoulder and arm, then there is a good chance it's coming from your neck. See your doctor if your pain lasts greater than 2 weeks. There are many conservative treatment options.