Hello, Thanks for trusting us with your health concern. Abnormal menstrual pattern is a common feature during the initial months of use of hormone contraception. Also, additional precaution is needed during the first couple of months to avoid failure. In the current scenario, you need to check for the presence of any erosion on the cervix, polyps of the cervix/uterus, infections of the cervix and vagina to detect the cause of the post-coital bleeding. You may need a sonogram of the pelvis to know the status of the pelvic organs and plan further management. Hope this helps.