I have to believe it's a pinched nerve somewhere. Pressure on certain areas of the body can cause the nerve to numb stop sending the right messages. The nerve may not actually be in your foot--it could well be in your back.
I never used to "believe" in chiropractic care and didn't understand why my husband went--he never got fixed--he had to keep going back for adjustments. But a couple of years after RNY, at a normal weight, but still having aches and pains I couldn't get rid of, I decided to try. I went 3X a week the first month, then tapered off. About a month into treatments (which only take minutes) I noticed truly profound changes. Once pain between my shoulder blades, which had plagued me for years, went away completely. Now I go only about 1x a month to keep my body in alignment.
I think chiropractic care is even more important for the person transitioning from obesity to normal weight. Our bodies got very used to carrying that weight and just losing weight does not straighten the spine and stop pinching the nerves. Vertebrae that is not perfectly aligned pinches the nerves running from the spine and out between the vertebrae, causing improper messages, which often show up as pain. Little other than chiropractic can fix it.
I will add though that sometimes there are other problems. My eldest daughter is a runner and her left foot used to go to sleep after 5-6 miles of running. It took breaking her ankle for them to figure out that a tiny bone had been broken long ago in her lower ankle and was pressing on a nerve that became inflamed as she ran and cuased the numbness. She had surgery to correct that bone when they took care of the break and it's been fine since then.
So, start with your PCP and go from there. Good luck.