Yes, yeast can and does cause a rash and itching/burning sensation. Typically the areas affected are the groin area and under the breasts. Sometimes under the belly if there is a bit of extra "fluff". Nystatin powder of Tegretol shampoo can work very well in these areas. Diflucan is a great drug for treating yeast that's "everywhere".
Colonoscopy won't cause yeast or GI problems, but is often done because of pre-existing GI problems.
Hope this helps!
Is it possible that a heat rash might be more likely? Get either a diaper rash ointment (like Palladin) or an anti fungal agent and it might clear up within hours