Neurontin is a good option. But it takes a little time. You have to start at a low dose, and work your way up over many days and weeks. But it has a good success rate for these types of symptoms.

Have you tried the OTC Biofreeze for the burning?

The skin biopsy would detect whether the small fibers have been damaged. Part of the test is to examine the condition of the fibers...including segmented fibers and those with swellings or other signs of damage.