--I suspect that B12 level may have some thing to do with this, as symptoms of B12 deficiency can mimic many other things.

I DON'T think this is an isolated small-fiber neuropathy. A small fiber neuropathy would affect sensory and autonomic functions, but, by definition, it would not cause muscular symptoms, as the small unmyelinated fibers underlie the sensory sensations of pain and temperature and many autonomic functions--they donot enervate muscle. But B12 deficiency can cause problems with both the peripheral nerves and the spinal cord, and given the variety of symptoms reported, it does sound as if you may have some spinal involvement. This could possibly be enhanced if there is any compressive forces in the spine or along the spinal nerve roots (have you had full neck/back MRI for disc bulges/herniations?--you are, after all, working a very physical job).