On Saturday, July 27th I gave unprotected oral sex to a stranger and swallowed his semen. He said he was clean and tested, but I have no way of knowing. I know most people don’t lie about this. Also, due to an unrelated infection, I began 500 MG of Amoxicillin 3X a day for 10 days. Anyway, i woke up today with an painful lymph node in my right armpit. So two things.

1. Would the amoxicillin prevent any bacterial STD’s from growing if they were present. 

2. Could HIV cause this swollen lymph node? If this is HIV, when is the earliest I could get tested and get an accurate result of my status (today is day 11). 

Oral sex is pretty safe -- of course not completely free of STD risk, but with a far lower chance of infection that unprotected vaginal or anal sex. You also are correct that most persons with HIV or with other STDs involving their lower genital tract (gonorrhea, chlamydia, etc) would know it and would not be untruthful when asked directly. So the odds are strong you were not at significant risk of any infection, regardless of the amoxicillin. However, as you suspect, that treatment did indeed further lower the risk of some STDs. It makes syphilis impossible, no worries there. Roughly half of gonorrhea bacteria are resistant to amoxicillin, so around a 50% reduction in the already low gonorrhea risk. Chlamydia rarely infects the throat even when exposed, but in any case amoxicillin would have been effective prevention.

A single enlarged or inflamed lymph node rarely if ever is due to HIV. The lymph node issues with HIV would result in multiple lymph node enlargements in places like the neck, groin, both armpits, etc; and there also would be fever, sore throat, and often a body-wide skin rash. Also, even if your partner has HIV (as noted above, it seems unlikely), the risk of HIV transmission penis to mouth has been estimated at one chance in 10,000. That's equivalent to giving BJs to infected men once daily for 27 years before you would likely be infected. Do you have any inflammatory lesions of your arm or hand on that side? Infected cut, hangnail, etc?

Those comments address both your questions. See a doctor if your lymph node problem persists. You could have an HIV RNA/PCR test at this time if you want further reassurance about HIV; that test is nearly 100% conclusive at 11-12 days. If you do it, you definitely can expect a negative result.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

Please note the forum rule against repeated questions on the same topic. This should be your last about this exposure, or similar events in the future or the timing of HIV tests after exposure. Thanks for your understanding. I hope this discussion has been helpful. Best wishes and stay safe.