Hi,
Without examination, confirmation of a diagnosis is difficult, but it seems like folliculitis or a boil are the likely possibilities for the sore between the anus and scrotum. But since there was unprotected intercourse, so herpes should be ruled out.
In that case investigations like culture of the virus, direct fluorescent antibody (DFA) studies to detect virus, skin biopsy, and polymerase chain reaction (PCR) to test for presence of viral DNA need to be done.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.