Hi & welcome.

There are MANY causes of PN. Your sudden onset can indicate compression, injury, autoimmune, or some other metabolic disorder. But it still wouldn't hurt to eliminate some of the more simple causes...like diabetes, B12 deficiency etc. MrsD will likely be along to speak more in-depth about that.

It doesn't sound like much testing has been done. I would consider requesting and EMG with the Nerve conduction test and maybe even an MRI to rule out compression/mechanical problems along the spine. Being a personal trainer, is it possible you injured something during instruction or exercise without knowing it at the time?

There is a skin biopsy that would confirm whether it it small fiber neuropathy, but probably best to take this one step at a time and eliminate things as you go.

Since you have some relief with the capsaicin, you might request some lidoderm patches...the relief could last longer.

It certainly wouldn't hurt to get some blood work for basic autoimmune, B12, Vit D, glucose, etc.