I would get tested for Vit D levels. This is turning out to be important for PNers and people with chronic pain/illness. Many on these forums find out they are very low when tested.

Also I'd get more aggressive with the B12. Injections often don't seem to work well. I'd do 5mg orally daily for 3 months and see if there is any difference. (take on an empty stomach so it will work best)

10 yrs is a long time...when long time issues are present, I'd look to diet as well. Gluten is the prime cause of long term neuropathy. But other foods may affect you. Nightshade veggies, dairy, soy etc. Doing an elimination diet carefully for one thing at a time, may be very revealing for you.

I take it you have had autoimmune testing to rule out Lupus and other autoimmune diseases?

If you are taking any RX drugs, look at them carefully. Many drugs can be culprits in PN.