You can have burning, stinging & numbness caused by elavated blood sugars even at prediabetic levels, if at some time you can get your sugars back down to normal ranges there is a good chance they can heal, it takes time though, nerves heal very slowly, mine took a total of 5 years, the numbness took the longest.
Metformin depletes b12 levels, B12 is important for nerve health so i would take some b12 supplements, R - lipioc acid helped me with the burning but it also can lower sugar levels, something to watch out for, another good supplement for diabetic neuropathy is [GLA] Gamma-linolenic acid at 480 mg daily.

good luck