Peripheral neuropathy symptoms for 3 years. multiple emg/ncv/skin biopsy negative. finally repeat skin biopsy way below normal. is this unusual?

Well sort of: Like I tell patients all of the time, if you have diabetes or a vitamin deficiency, then pinning down the cause of a neuropathy is easy. Anything else can be quite a challenge and there are literally hundreds of causes for neuropathy otherwise. I'm sure at this point you had a thorough work up, but seeking quaternary care (e.g. Mayo Clinic) is not inappropriate at this point

Have encountered this on occasion, especially with underlying arteritis/ vasculitis disorders which do not present with length-dependent small fiber neuropathies. Several unusual causes can be implicated, and a series of blood and urine studies may well reveal etiology. Discuss with your neurologist. Further evaluation at Mayo Clinic is a wise choice.