Hi New, and

I agree with zorro's comments.

There are so many variables with PN in general, and with each individual case. One constant seems to be that regardless of the cause, neurogenesis takes a loooooooong time. We all feel that frustration when this cussed thing hits us. Your story reminds me of that corny old joke:

Patient: Doctor, it hurts when I do this.

Doctor: Then don't do that.

(I've actually had that happen. )

IME, doctors tend to believe in likelihoods rather than possibilities (and I often do the same). They begin with the most likely cause of a problem, and work down, verifying or eliminating, until they reach a point they feel is unreasonable to pursue beyond, at which time they admit they don't know, give up, or pronounce something "idiopathic". Often they're right; they/medicine don't/doesn't have all the answers - we're all still learning.

There are a lot of treatment ideas and experience on this site, but you may have to dig/search a bit. The RLA & B-complex is one of the best; your B12 level seems good, but keep taking it anyway. You might consider adding B5, even though it's rare to be deficient in it:
http://www.diabeteslibrary.org/View....ntothenic_acid
(It's helping me even though I'm not diabetic.)

I think for most people on this site, treatment is a process - and a grand experiment (grand in the extensive sense). No quick/easy answers/fixes. Hope, but no guarantees. PN is a rude life-altering experience, but one that can be adapted to and lived with.

Doc