Hi Sarah.

Have you ever been tested for B12 levels?
If not I'd get that done ASAP.
I'd also get a Vit D test when you get the B12 measured.
New research is showing Vit D very low in people in US who don't get outside in the sun enough.

Since you have had this for so long, I'd also wonder about
Gluten intolerance, or some other food reaction.(like MSG reactions)
Also thyroid...but since you have 3 children, I'd suspect that was checked with each child during your pregnancies?

You don't have numbness? pins and needles?

Some people with congenital Arnold Chiari Malformation have odd sensations, but you would most likely have other signs than just these you describe.

Have you ever tried a menthol containing lotion or ointment?
This is cooling and blocks burning nerve sensations temporarily.
Biofreeze is one form that is high in menthol and a pleasant gel that is non greasy.

With PN... one has to go thru a long detective process to find a cause and what may help. So you have to be willing to do that.

edit to ask.... do you have REDNESS with the burning? There is a condition called erythromelegia...which responds to magnesium.
If you are very low in magnesium, this might be a factor. But there is typically redness that accompanies the burning from this.
Dr. Jay Cohen MD has a book on magnesium in fact. He had erythromelegia himself, and describes how he fixed it for himself, in the introduction of that book.
http://neurotalk.psychcentral.com/post525853-154.html