I've had mild Osteoarthritis (OA) in my left shoulder/collarbone area for a number of years and coincidentally developed Peripheral Neuropathy (started left arm & both feet - now full body). My left elbow was tested a few years ago for a compressed ulna nerve - results negative - and the numbness and muscle wasting in my hand were attributed to the PN.

At night if I sleep on my right side I usually have my left arm either across my chest or along my body. Recently I've had increased pain in my left shoulder, extending down my arm to fingers, and frequently my arm will go entirely numb. By chance one night I stretched my arm behind my back, (somewhat awkward and uncomfortable). Within 15 minutes the pain and numbness was gone.

My conclusion is that it is a compressed nerve, but not in the elbow, instead in the shoulder (which was never tested). By stretching the arm back it releases the nerve but having the arm center or forward causes the compression. It may also be affected by possible osteophytes (bone spurs) near the joint.

I also do regular PT and recently some of the exercises (particularly Lateral Pull Downs), have caused increased pain in the arm and hand. I've added reverse arm stretches to my routine to help keep the nerve free. So far it's doable. I see my GP in a couple of weeks and will request a referral to get it checked out by an orthopedist.

Baba222 I hope you're able to get some help for the tendinitis.
Thanks MrsD and others for the supplement suggestions. I'll keep them in mind if it gets worse.