Ask them to take a look at viruses. Viruses like herpes zoster and HSV1 can create nerve inflammation. And sometimes it can appear with or without a rash.

I contracted a viral illness that started with a severe headache and jaw pain and nerve pain.

Ask the docs to run a viral blood panel...including varicella zoster IGG and IGM, HSV1 IGG and IGM, EBV and HHV-6.

Ask the doc for a trial of valtrex or you can try l-lysine (over the counter) to see if it gives him any relief.