Random rash!?!

To start off, I'm not pregnant. (As far as I know) but this random rash appeared. Does not hurt or itch whatsoever. I recently traveled from Washington to Arizona and was wondering does this look like a heat rash?? Went to my doctor he had NO clue what it was so he wouldn't treat it. He is sending me over to a dermatologist to get a biopsy next week?! By the way, the rash is only on my stomach and chest. That's literally it.