Vaginal bleeding after sex gets complicated fast because there are lots of different spots the blood can be coming from, and it's almost impossible to tell on your own, without the tools and expertise of a medical professional. Dr. Aimes-Oelschlarger said she breaks it down into four different locations: the entrance of the vagina at the hymen, inside the vagina (on the walls or in the septum, if you have one), the cervix, and inside the uterus.
As Dr. Aimes-Oelschlarger explained, the most important thing to pay attention to is the volume and rate of the bleeding. Like any other wound, a lot of blood is never a good sign. "Most postcoital bleeding will be pretty light, except for the septum," she said. "It's pretty rare to have really heavy bleeding unless there's a laceration in the vagina. The heavy bleeding, where you're soaking through a pad every hour or so or passing large clots, those patients need to be seen very quickly."