DS has had a few fungal rashes - one was on upper shoulders and made his skin full of little white patches. His LLNP said to use dandruff shampoo on it and that did work. If the cream your dr gave you doesn't work you could try that. We typically try antifungal spray first and it usually helps. I always check his tongue to see if it appears internal (not even sure that's a valid way to tell, ha) and so far it's looked good.
I hope you get some relief soon. Also, I strongly second the idea to avoid sexual contact until it's truly gone or you'll be in a heap of trouble.
Parent of teen DS w/ CDC+ Lyme test Nov 2015, late stage Lyme + mycoplasma (stubborn/lingering), bartonella, babesia. Currently treating with pulsed antibiotics, moving toward maintenance and headed into remission - no sick days this school year yet
Website I started: ParentsofLymeKids.com
aka Lyme Disease 101 for Parents