I'm not sure if this will be very helpful Catherine, but as an MSer I get this sort of pain in my legs from time to time. It's possible your arm pains might be similar, although obviously with a different origin.

Plain Magnesium (not the one that's mixed with anything like Zinc) is available over the counter and can often give relief. It does sound like you might be having muscle spasms, and Valium (Diazepam) is another medication that can possibly help. It certainly wouldn't hurt to give them a try.

I do hope you find relief soon as I'm sure you don't want to be taking narcotics long term.