Heather Corinna replies:

The most likely possibility is that what you're seeing coming out of your vagina is simply semen: the sexual fluid which carries sperm.

The vagina isn't a bottomless pit: it ends with the cervix, the base of the uterus. The opening to the cervix -- called the os -- is incredibly small. It can dilate to a much larger size when a person is going to deliver an infant, can be dilated for medical procedures by a healthcare provider, and it does get a little bit larger during certain times in your fertility cycle -- it's a little more open during menstruation and ovulation -- but overall, it's seriously teeny.

Sperm can get through that opening, because they are microscopically small, as can some bacteria, and your menstrual fluids can make their way out, but semen as a whole, doesn't go in there. It will pool in your vagina when ejaculated, and then run out afterwards. A lot of that will happen within a few hours after, but the vagina cleans itself in a cycle of every few days, so you can often see (and smell) some different-looking discharges from your usual for a couple of days after unprotected sex. Sometimes, people who are trying to become pregnant expect that for pregnancy to happen, all that semen needs to stay in the vagina. What they're missing is that sperm is the important part of semen with pregnancy: the rest of those fluids are basically just there to keep sperm viable and to help get it to the cervical opening. In other words, semen is basically just giving sperm a ride: it doesn't need to stick around once it drops the sperm off.

Of course, too, if you're using a lubricant, that can also be discharged, and there's your own natural discharges which make their way out as well which you're probably already used to seeing. For someone with a genital infection which can cause new discharges, or greater discharge -- like bacterial vaginosis, a yeast infection, trichomoniasis or other infections -- they might see those, too, but symptoms of a sexually transmitted or genital infection tend to need at least a few days -- and often longer -- to develop. You won't be seeing STI symptoms the next day after sex with nearly all infections.

However, since you did have unprotected sex, you'll want to make sure you do schedule a screening for infections in the next month or so, and that you keep current with those every year after you first become sexually active, even when you are using condoms, though it's obviously even more critical if you aren't. And if you do not wish to become pregnant, then you may want to consider getting and using emergency contraception as soon as possible: you have within 120 hours of a risk to use it, but the sooner it's used, the more likely it is to be effective.

Lastly, if you and your partner have not been monogamous for six months, using safer sex practices during that time, and both have not been tested and cleared for all STIs yet, just understand that you are both taking risks of infections with unprotected sex. As well, if you're not ready and willing to become pregnant right now, sex without using a reliable method of birth control -- be that condoms, birth control pills, a cervical barrier or some other solid method -- isn't a great idea. So, if you want to reduce those risks, you'll need to have a chat with your partner about how to have sex together with safer sex and birth control, and by all means, if you find yourself with a partner who won't cooperate with that risk management, I'd encourage you to manage your risks yourself by showing that partner to the door.

Here's some extra information for you on all of this: