Doctors I need to solve a doubt. It turns out that about 1 month ago I practiced oral sex with a stranger, but there was no ejaculation in my mouth, and then I did not observe liquid preseminal in his penis, but 3 days later I realized that I had an ulcer in my mouth, and I worry Who has had the ulcer when I practice oral sex and I have not noticed, is there a risk of HIV transmission? Help please i'm very scared