You have classic presentation for SFN and you should find another doctor/neuro!! The skin biopsy is not necessarily done only on places where pain is at. The most common place for pain is the bottom of the feet yet NO skin biopsy is ever done on the bottom of the feet!!

You really need to so another neuro with more experience...and the skin biopsy would be an appropriate test for you (with site being done at ankle, just below knee and thigh (to determine length dependent or not).

There is literally 100+ causes of neuropathy and you just have to work through various testing (most obvoius causes first) to see if you can determine which is causing yours.