I had an unprotected vaginal exposure on the night of 10/17 with a heterosexual female. The next morning when I was getting ready to leave, she received a text from another man who she had sex with two weeks before I did, who told her that another female texted him to test for trich because she had that, and when he had a full panel on 10/15 looking for trich, he tested negative for everything but he tested positive for syphilis. Again, the last time she had sex with him was approximately 2 weeks before I did on 10/17. Worth mentioning is that I also had sex with this girl on 9/17 which was brief unprotected vaginal. 

Hearing this, she immediately got tested with a full panel on 10/18. All of her tests came back negative. Regardless, she received a penicillin shot on 10/19. When I left her place on 10/18, I was able to consult my doctor who prescribed 10 days of doxycycline, which I started same day. On 10/21, I had a full STD panel myself which was all negative. 

Based on what we know, the guy is heterosexual and has sex with women, not men. He also claimed to never have had symptoms and did not have any chancre sores when he had sex with the girl. Her gyno doctor believes he may have had a latent infection for some time which is why she doesn't have it. My questions are:

1. What additional tests should both myself and the girl have from here?

2. Should I have sought PEP in this situation even though the girl tested negative for HIV and the guy also tested negative for HIV? 

Thank you sincerely for your assistance with hosting this forum.

Your partner was managed perfectly.  The fact that her test after she was notified was negative means that she could not have transmitted syphilis to you- persons with negative syphilis blood tests virtually never transmit syphilis to partners.  At the same time, it is appropriate that she got a preventative shot of penicillin although the doxycycline your received would have prevented syphilis in case syphilis had not been established but was developing.

In this situation, since your partner did not have syphilis, you did not need treatment although your doctor chose to do so, presumably out an abundance of caution.  The doxycycline regimen you were prescribed would both prevent developing syphilis and cure syphilis if you had it (which you do not)

Regarding your specific questions:

1. What additional tests should both myself and the girl have from here?

Your negative STI panel prove that you were not infected.  There is no need for additional testing and no need for testing or treatment for your regular partner.  You are in the clear

2. Should I have sought PEP in this situation even though the girl tested negative for HIV and the guy also tested negative for HIV? 

No, persons with negative tests do not transmit HIV.  There was no need for PEP.

Thanks for your questions.  Everyone involved here did just what was needed and you are all in the clear because of it.  If anything is unclear, please feel free to use your up to 2 follow-ups for clarification.  EWH

Based on this fact pattern, do you think I need to worry about someone being in a window period for HIV or anything else even though everyone here involved tested negative? As far as infectiousness/transmissibility. Thank you. 

Once again, I urge you not to worry.  EWH