I know exactly what you are going through. I went ,for years, back and forth to numerous doctor's only to discover I had an autoimmune deficiency disease, called, Polymyositis. Had biopsy on right thigh, because I could not get out of bed one morning because I couldn't feel my right leg. I slid out of the bed to the floor and crawled using my arms to propel myself. The pain was horrible.Then an hour later my leg was fine. My wife dragged me to the doctors, 🙂 ( men we are stupid ) And so started my journey of endless and " I can't find anything wrong" dance, that finally ended with a savvy young doctor, who found the problem. So when my polymyositis is not in remission it's, some exercises and steroids, only temporarily, until it's back in remission, which could be days or weeks.
No cure, for this, but I can say, that I have been in remission, for 5 years now! (crossing fingers) That's all I can do.
John