I have another recommendation for you. Since your skin punch biopsy was normal you might want to investigate the new MRI procedure to evaluate the dorsal root ganglia (if you haven't done so already).

This post explains the procedure:
http://neurotalk.psychcentral.com/thread147771.html

Damage to nerve cells in these ganglia, can become permanent in some people. The nerve cell growth factors that repair damage to the roots, are missing genetically in some people.
There is research in this area recently, looking into repairing this damage with perhaps stem cell treatment. The damage can come from viruses like H. Zoster, or toxic drug treatments.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3287412/
This is a new interesting article on this subject.
This article mentions NMDA antagonists, and magnesium is one.
Just make sure your magnesium is an absorbable type and not
the OXIDE type. OXIDE is a poor form, and very little is absorbed from it. Other NMDA antagonists are Dextromethorphan (which cannot be used with SSRI or other antidepressants (Wellbutrin excluded). Also the RX drug Namenda does work for some people. Some of our RSD posters use it.
More on NMDA antagonists here:
http://en.wikipedia.org/wiki/NMDA_receptor_antagonist
MSG --a common food additive-- is a NMDA stimulant, so avoiding it
may help with some pain issues. Some people are very intolerant of it, and others not.

If you are using high dose B6, it might be a good idea to cut back on that. Some people posting here over the years claimed to be very sensitive to B6. Don't go over 50mg a day, and perhaps even less than that. The official recommendation is less than 100mg a day but some cannot tolerate that. If you take a B12, I'd stick with the methyl form as you don't know if you have a genetic error of methylation. And take that on an empty stomach. It is best to have blood work to guide you and show if you even need to take it at all.