I feel for you, Skywalker, not being able to try more than one pain specialist. I've been to a rotten one who was fired later by his famous clinic, and I've been to a reasonable, good one too. The good one told me to just continue taking demerol when in pain, which I was only on a minority of the time, and I had shown that I had no interest (over years) in taking demerol when I was not in pain--that is, not addicted. As I can't take any other pain med without severe side effects, that appt. was primarily to check up to see if he approved of the demerol, which he did, said I was doing just right with it. I once tried another pain med just to see if I could take an alternate one, which experiment was approved by my doctor. I took one Oxycodone. It gave me a fever four six points above normal for four hours, and had me trembling on the floor until it wore off, after which I was none the worse for wear.
You don't have the "coverage" to do this kind of "trying things out" and I think that is a crying shame.
Pain can come from other stuff than MS, of course, so that complicates things a lot.