But i do have mouse arm, the muscles behind my right shoulder blade are completely knotted.

I deal with it by being ambidexterous. I now use both hands for mouse and alternate between them when I am tired.

I type 8 to 10 hours a day as a transcriptionist.  I have had carpal tunnel and tenosynovitis.  I use Voltaren cream, it is available without a prescription. I rub it into my wrists when I feel soreness and it lasts several hours. If you need a stronger one than the one the drug store sells, you can get a prescription for a stronger one from your doctor and they mix it up at the pharmacy.  Works great, not systemically absorbed so no ulcer worries with the oral versions of NSAIDs.