Hi Mel, i am really sorry to read that you are having the burning feet problems now & i hope that the B12 supplementation yields good results for you soon.
It takes time for the nerves to heal, but our bodies have a remarkable ability to repair itself, once given a chance to do so.

The numb toes, were of course signs of damaged small fibres, as the small fibre's job is to give information to the brain as it interputs feelings of pain, heat, cold & vibration which you really did experience their reaction to that podiatrist vibrating machine.

As to " what or why " started them burning all of a sudden ", someone else may be able to explain it better than me, but all i would say that your nerves are telling you in a more noticeable way now than before, that they are damaged & perhaps more than were before.

I would not class coffee as as neuro toxin especially at only a couple cups of coffee a day, other things like heavy alcohol, lead, arsenic etc. are what you call real neuro toxins that do really affect our nerves badly.

You guys in the US are so lucky to be able to get Methylcobalamin so cheap and easy, i think the others will say 2 mg per day is enough and a good amount to take, which it is, but personally, if i could get this gold so readily i would take 5 or 10 mg a day, but thats just my choice only.
I know you won't muck around and you will get this problem reversed in no time.
take care
Brian