small fiber neuropathy

I was just diagnosed with small fiber neuropathy.  Now the Dr. is trying to figure out what is causing it.  I had a neg tilt table test done, my b12 is low but the methosomethingacid is normal so he doesn't think it is a b12 issue, and I have to go get my blood work done again tomorrow to check some other things, one of which is my blood gloucose but I don't think it is prediabetes since I have a meter at home from having gestational diabetes 15 months ago and I have checked often since and I am always in the perfect range.  I also have been diagnosed by a cardiologist with sinus tachycardia.  Does anyone have any suggestions on what this may be???  I have alot of numbness in my feet, and my feet, legs, arms, hands and face burn alot.  It is worse with heat and seems to be affecting me more with my mentral cycle too.  Thanks for any advice!  :)

[jojo998]

my mum also has been diagnosed with small fibre neuropathy and every med that the doctor has been giving her her has caused her headaches and makes her tinnitus worse, she is 81. Has had all the tests done, they cant seem to find out what caused it. just started to take alpha lipoic acid and a vitamin b100 complex yesterday. waiting to see if they work.