My thought was any kind of flora/fauna (bug bite, contact) that may have been overlooked or unknown, whether related to the rash or not.

E.G.: In the Western US, there's a disease known as Valley Fever (Coccidioidomycosis, which is probably why they call it Valley Fever! ) (This has nothing to do with PN or rashes - I'm just using it as an example), that's well-known by all the doctors in that part of the country. It's caused by a fungus in the ground. It's usually not too serious for humans (but can be), but it can be devastating to dogs, especially those that rout around in the soil.

But most doctors in the Eastern US have never heard of it (by its colloquial name, anyway) since it's not endemic in the East. People who visit the west for a period of time may contract it, but when they get home, and symptoms manifest, their doctors may be stumped, not knowing to look for it.

You said you moved recently? Does the timeline fit with the onset of your symptoms? Is your new location geographically removed enough that something environmental could be at work (you mentioned a friend who presented similar symptoms)?

I'm jes' spitballin' here....

Doc