When you have intercourse with a condom on the sixth day of your period, the first thing that happens is that when you have your period, the tissues are loose. When you have intercourse, the endometrium becomes excited and the bleeding increases, resulting in a low menstrual flow and a heavy menstrual flow. Some women may also experience abdominal pain or high fever, and since the fallopian tubes are connected to the uterine cavity, endometrial tissue may reach the pelvis with the fallopian tubes during intercourse, which may cause endometrial tissue to be planted in the pelvis, resulting in endometriosis. Endometriosis, which can cause chocolate cysts or adenomyosis, can also affect the chances of conception in the future, and intercourse during menstruation can cause vaginal inflammation as the uterine opening is open. At this time, intercourse during menstruation is forbidden, otherwise it may cause irregular menstruation and infertility.