Hi and welcome, I can't understand them saying your Idiopathic or Prediabetic,
as being prediabetic is a definate cause of PN and idiopathic meaning no cause found
I am glad to see that you are working on your Prediabetic state, because you don't have to have full blown diabetes to get PN, the peripheral nerves will regenerate if they are in the right inviroment, i was diagnosed as being prediabetic as the cause of my mostly small nerve damage and its taken me about 3 years to get were i am now, that very close to a full recovery.
Exercise is a problem when your feet hurt so badly, but i found that just simply walking up and down a lane in our local swimming centre is a great exercise, it doesn't hurt your feet, none weight bearing and its a great cardio exercise too, i used to go to the pool early when it first opened and there were plenty more people doing the same thing for all differant medical problems.
If you do all the right things you can reverse that prediabetic state and hopefully your nerves will start healing, its a roller coaster of a ride with at times worsening of symptoms but the end result are well worth it. it does take time but they can a do heal.
I was also low on B12, and have mainly supplemented with Cynocobalamin, some Methylcobalamin and shots of Hydroxocobalamin [ Methylcobalamin is the preffered B12, but if you can't get it there is nothing wrong with Cynocobalamin.
good luck
Brian