Did the small mark appear immediately after the encounter or a week later?
I share your pain, I did the mistake of allowing a stranger to go down on my for a minute and ecjeculated into his mouth. I have been waiting 15 days now, actually did a visit to my local std ward and they took urinal and tissue sample from under my foreskin. That is I think for determining if I got Herpes or Clamidia but then I have to go at 6 weeks from exposure for a full urinal and blood check, I will have them check all including HIV even though chances are considered zero for HIV transmission from receiving oral.
Duration of oral sex? The chance of getting stds from oral sex is very low and the onset of symptoms within a day is probably too soon for any possible stds. I will assume it's probably irritation from soap but I would suggest getting stds check for NGU and gonorhea. Those were the common stds to be contracted through oral sex and there are curable with antibiotic.
Hey i feel your pain. I going through the same thing as well, i know how it feels to be depressed my best advice is to get tested and dont stress too much. Get some blood work done and pray for the best. BBest of luck