I have a form of a myotonic dystrophy (MD II) which causes similar muscular issues you are facing (pain, weakness, muscles not relaxing - staying tensed) I also have pain issues that aren’t easily managed because of it.
I also have some other conditions that makes the meds list I can take short.
My neurologist (Mayo) tried Baclofen but we didn’t have much luck.
I know it is not possible for many folks to find a way to stretch. I had some home health care last year. They showed me ways to stretch even if you cant get out of bed. I have found that a good daily stretching routine has helped with mobility and some pain. It can help with the stiffness and not wanting to relax the muscle which likes to stay contracted.
It is definitely hard to find docs that deal with these conditions - many have never heard of it.
Here is a link - which you have already looked at but might be a good starting point for finding something in your area Ike an
MDA Care Center. Mayo here in Jacksonville has one. The MDA.org site - https://www.mda.org/disease/myotonia-congenita has some search tools to find them in your area.
Hope this might help.