I'm going on 30 years of various nerve maladies. Finally a supplement came thru which is helping whole body inflammation caused by high uric acid levels (gouty arthritis).
Just keep pushing for nerve tests and try various doctors until you will get one to work with you for the long haul. One who will "learn your body."
Sounds like nerves being crushed from L3-L5. So make sure an orthopedic surgeon is in the mix of your doctors. It also sounds like diabetes and neuropathy.
nerves being squished cause me "on fire" and "feet in pain" and numbness.
Right now I have an onfire ache in a leg area which has been numb for 14 years! It COULD BE the nerves dysfunctionally growing back after relief from lumbar surgery in 2018. It takes 10 years sometimes for nerves to regenerate. When they do - maybe I wish they didn't?! Try topicals. Try nerve meds. Try acupuncture and MFR (section here on it) Try massage and symptom relief in the meantime. good luck!