I could be wrong on this but I think EMGs start turning up positive if there is large nerve fiber involvement (motor nerves not just sensory). I have had SFN for almost 20 years and my most recent EMG was still negative. I'm sorry you're struggling with foot pain, it's really horrible, I know. I have it too and gabapentin made life bearable for me. I'm not trying to push it on anyone and I know that everyonne responds differently to it but I wanted to live my life as normally as I could and for me the side effects weren't a problem. I did have a lot of fatigue (still do sometimes, being in pain is very tiring!) but it got better once I got used to the drug.
Wishing you all the best!