The most common causes for vaginal bleeding after sex both start in the cervix, which is the narrow, tube-like end of the uterus that opens into the vagina. One of those causes is cervical inflammation, or cervicitis. It can be ongoing and totally harmless, or it can happen because of a sexually transmitted infection that you need to get treated, like chlamydia or gonorrhea. Both types of cervical inflammation can cause bleeding after sex. A second common reason for bleeding after sex are cervical polyps. They are growths that are usually small -- about 1 to 2 centimeters -- that often appear on the cervix where it connects to the vagina. Most aren’t cancerous, and a doctor can remove them during an appointment.