I would ask for the Vit D test. We had a young woman here a short while back who just had her 4th baby, and when she started to exercise after delivery, her feet became very painful.
Her Vit D level was like-- 10 or close to it, very low.

I have to wonder about "after the baby was born" things started happening. Either this may be damage to nerves in the spine from an epidural? strain on the leg nerves from delivery?
or an autoimmune flare of some type after delivery?

Nothing in the hands? Metabolic problems would show up in both hands and feet. My thyroid issues were severe in my hands during pregnancy.

Pregnancy takes alot out of the mother. EFAs the baby uses to form its brain, come from Mom. Then Mom can be low in these essential oils our bodies use to keep the nerves running well.
Fish oil, Flax oil, and evening primrose can help. If you are having very dry skin after delivery that might be a sign too.
Our American diet is often very low in these. But now we have "smart foods"..
Omega -3 eggs
Smart Balance peanut butter and spreads
Omega-3 mayos now
Flax in some cereals, etc.

You can try to use these to help as well. There are some Omega-3 enriched prenatals out there. Did you use one of those? This one is over the counter:
Expecta
http://www.enfamil.com/app/iwp/enf10...1&r=3462860705
and
http://www.mayoclinic.com/health/pre...tamins/PR00160

See what the rheumy says. There are other tests for inflammation, like c-reactive protein, ESR which are blood tests.
I've had elevated ESR in the 25 range for many years, but negative on ANA and RA panels. It remains a mystery for me.
I do have osteoarthritis tho, and some seasonal allergies, and that might be a factor, for those tests. Were you tested for heavy metals?
Arsenic in water or pressure treated wood exposure or ant killers can be a culprit. Spraying pesticides on the garden?

In the meantime, good conservative shoes, and a visit to a podiatrist to see if there is some mechanical problem in the feet, compressing nerves, etc might be a good idea.

PN is like a detective story... may take some time to find the cause. Remember some antibiotics you may have used in the past, also cause it. (Cipro, Flagyl, Levaquin, Avelox).