Have you been tested for hhv-6? This same thing used to happen to me, I got tested for 1&2, both negative. So I put it off to just irritation from sex, also thought maybe it was my laundry detergent possibly causing an allergic reaction. Then I got a round of sores on my upper thigh out of the blue and went to the doc. They told me it was shingles (hhv-6). I asked them if it was sexually transmitted (I never had this problem until a few months after being sexual active with my cheating ex). He told me it was highly unlikely, but that viruses can be transmitted all sorts of ways. So I really don't know if I got it from him or at some other point in time and it just activated then. I've had two other partners since him and neither of them ever had an issue, and I told them both before hand just in case. I would go to the doctor and ask about hhv-6. This doesn't sound like a yeast infection