Well there are now better guesses as to what is going on. Gina got to have a play this time - first time she couldn't even touch my back without flinching. The current guess is that there is sheath damage to the nerve that runs from the spine to under the shoulder blade, to the left arm. It explains why I couldn't find a rest position, and it explains the pain.
Voltaren 50's from the doc, and Mycendol means that I actually got sleep over the weekend. I'm off to Gina's in just a few minutes to get cranked again. I made it to work, and got through the shift okay. However, I'll have to change my pain management - I just hit the recommended limit on Mycendol and have no interest in back effects - but I also have a great interest in making sleep possible.