The best way to approach this problem in a younger person with no thyroid markers, or diabetes symptoms with blood sugar anomalies, is to go back to before you had the initial symptoms.

What were you doing then? Any antibiotics in the year leading up to this taken? What were they for and their names. Any vaccines? What hobbies do you have--any with paints, solvents, furniture resurfacing, gardening with pesticides, etc.
Any allergies or reactions to something in your environment?
All details may leave clues. Knowing what triggers you then points to what you may be able to do the stop it or reverse it.

Any drugs you used, RX and recreational? Nitrous oxide at the dentist? Alcohol consumption? Toxins in the environment may be heavy metals like lead, arsenic (well water), cadmium, etc.

Your diet and exercise routine. Shoes? any foot problems?
Diet is important because foods can trigger burning, tingling and nerve symptoms. Gluten is the biggest offender. But nightshade veggies (tomatoes, potatoes, all peppers), can trigger discomfort in some people. MSG in processed foods is a biggie also, because it triggers pain receptors. Some foods are actual histamine releasers. They may be blocked by Zantac, and Benadryl.

Do you have good days? What was going on the day before a good day? Do you have pain 24/7 or only sometimes?

Do you have relatives with PN symptoms? This would suggest a hereditary component.

Are your feet involved? Or only the legs? If the legs only, have you had spinal testing to see if you have compressions along the lumbar, etc?

Some nutrient deficiencies give symptoms. Low B6, low thiamine, low B12, low D, imbalances between calcium and magnesium.
Most Americans are low in magnesium--up to 70% of us.

Medically after all the typical stuff is ruled out, then there are medical tests for antibody status (elevated peptides in the blood make it thicker and sluggish), and autoimmune studies to see if you have Lupus or Sjogren's, or some other autoimmune issue.

You doctor is not likely to do this detective work in detail...it is really basically up to you to do it all.