Hi Munsterman,
Sorry to hear about your predicament. I'm not a doctor nor am I in a position to offer any other medical or medical type help. But your description of your early symptoms struck a chord with me.
A couple of months ago I developed an ache in my arm, not overly painful nor restrictive except when my arm was raised above shoulder height. I put this down to the aftermath of an energetic couple of days removing wallpaper, washing walls and applying paint at the time. I rested my arm and expected the problem to rectify itself in a few days.
However, the problem is still with me, niggling away. I haven't done any painting or the like since, nor would I feel able. I wouldn't feel my arm could cope without aggravating the situation. Raising my arm above shoulder height or backwards from shoulder height is as difficult as day one and leaning on my arm or shoulder can be uncertain because of a leftover slight weakness.
To date I have not sought any "professional" advice or treatment. It occurs to me that the problem might be neurological rather than muscular or skeletal and I wonder if this might be the same in your case? I mean, some nerve damage as opposed to a pulled muscle ir sprain, etc?
As I said, I have no medical background but offer this suggestion for your consideration.
Most of all, I hope you get the problem rectified before too long.
Regards, Ash