The arms that are fatigued. I have that, especially if I do something repetitive with those muscles. It does not seem to be the arm itself, but seems to be coming from the area across the back, where nerves, tendons, muscles and ligaments attach (area around the scapula). Sometimes it bothers me to the point where I cannot carry my purse.
I know you need to see a neurologist, but I will tell you what helps with this for me. Trigger point injections in the areas I described above. A tiny bit of cortisol, used with lidocaine to numb the area, is injected in those areas. The cortisol helps with inflammation in the area.
In our area, pain management docs do a lot of these, but I know this can also be done by doctors in a number of other specialties.
By the way, regarding your comment on Fibromyalgia. My old Internist told me he felt that this diagnosis was what Rheumatologists come up with, when they cannot figure out what is really wrong... He also said he felt that this would eventually be proved to be a connective tissue disease... Boy, my old Rheumy got defensive when I repeated that to him...
Guess I wasn't very tactful, huh?
Cathie