1 - What are the chances of catching Syphilis, Chlamydia, or Gonorrhea or HIV?

2 - Will taking Doxycycline be effective to reduce against any STI'S?

3 - Do I need to be tested ? If so what are the timelines for the above infections?

4 - Should I refrain from having sex with my partner until tested.

5 - Do  need any other medications to prevent infection?

Thank you

You say nothing at all about your partner. Do have a sense of her sexual history? Most sexually active women have no transmissible STI at any point in time; and even when infected, most single vaginal sex exposures do not result in transmission to the partner. Without more information to suggest she is likely to be infected, I would strongly advise against doxycycline. A far smarter plan would be to first, learn more about your partner's risks; wait a few days to see if you develop symptoms like penile discharge, painful urination, or genital sores. Alternatively, speak with her about her risks, and perhaps go together for testing for gonorreha, chlamydia, syphilis and HIV. Maybe you'd find she is just as concerned as you are:  after all, in general women are at higher risk from there male partner than you are from her. If you both test negative, you would know neither could have infected the other.

1. Chance of infection with these STIs? Probably low, but need more information to judge the risks. (For HIV, probably under one chance in a million.)

2. Doxycycline would reply prevent only syphilis and chlamydia.

3. Need for testing also depends on better understanding of the chance your partner is infected.

5. I would advise against doxycycline and any other antibiotics at this point.

I'll be happy to comment further if you would like to provide the crucial missing information.

HHH, MD

But I'm not you and you'll have to make your own decision. Another option, knowing where you are, is to get in touch with your nearest NHS GUM clinic for world-class evaluation and advice from experts who undoubtedly understand the local epidemiology of STIs and risks for an exposure like yours far better than I can judge. Or one of the excellent private sexual health clinics, like London's Freedom Health.