--have you been worked up and tested?

From what you're saying, it sounds very much like either there is some sort of brain/spine thing going on (have they done full MRI with and without contrast, any evoked potential testing, lumbar puncture, to look for central nervous system demyelinating disease, and/or an infectious process such as you suggested?), and/or some sort of rheumatologic or connective tissue/vascular autoimmune disorder (have you had extensive work-ups for the family of anti-nuclear and related antibodies?).

Trouble is, it's very hard to distinguish a peripheral nerve problem from a central nervous system one--they can produce exactly the same symptoms, and usually diagnoses are arrived at (if they are arrived at) by exclusion.

BTW, a "small-fiber" neuropathy is by definition NOT demyelinating--the small-fibers are clinically defined as the non-myelinated sensory and autonomic fibers axons. It's certainly possible to have neuropathy of the larger, myelinated fibers (which include all motor fibers and larger sensory ones that subsume the sensations of vibration, position, and mechnaical touch) and of the small unmeylinated ones (which sumsume the sensations of pain and temperature) simultaneously.

Nerve conduction studies and EMG cannot diagnose a small-fiber problem; those nerves are simply too small to be measured using the current technology. (Often, even large fiber syndromes are not noticed by these tests until the damage is quite extensive.)