Period 10 days late finally came light but painful for 3 days,1 day after it ended i had dark brown/black blood ?

Irregular period: Many things cause irregular periods. If you were having unprotected sex it is possible this was a mild miscarriage. It could also be due to normal life stressors. You should reset to a normal period within the next two months. If you miss your next period, take a home pregnancy test. For any other concerns please see you doctor.