The bleeding on the 12th day of ovulation is considered to be caused by pregnancy. When you have intercourse during ovulation, if the sperm and egg unite to form a fertilized egg, it will stimulate the uterus and cause vaginal bleeding and mild abdominal pain when it comes to bed. The bleeding may be caused by miscarriage, you can go to the hospital to check the HCG in the blood, if you are sure that you are pregnant, consider the bleeding caused by miscarriage. It is recommended to eat more vegetables and fruits and keep the bowel movement smooth.