This could be a couple of things! First, I’m assuming this is penis-to-vagina sex without a condom. There is something called bacterial vaginosis that can affect vaginas regardless of sexual history. It’s caused by too much of one type of bacteria in the vagina and produces a strong fishy smell (as well as itching or abnormal vaginal discharge). When semen comes in contact with this bacteria, it can actually make the smell stronger! So this might be a sign that you have a small infection of the vagina. It’s very easy to treat and shouldn’t be embarrassing to share with a doctor (again, because it can happen to people who have never had sex/it’s not necessarily related to sex at all).

The second thing it could be is your partner’s semen. Depending on their diet (like if they ate a lot of asparagus, meat or fish) or if they have an infection, semen can have a strong odor. You could try some detective work on your own and see if your partner’s semen has a smell when it’s not in your vagina. It won’t give you a definite answer, but it might get you headed in the right direction.