Light spotting when im expecting my cycle or a week after it is over. it only last for an hour but it comes with regular menstrual pain what is this?

Endometriosis: The most common cause of soptting before or after the period, that is accompanied by pain, is endometriosis. Endometriosis is a condition in which the endometrium, the tissue that makes up the lining of the uterus, gets into the pelvis and implants. Other causes of spotting around your period can be hormonal or polyps in the cervix or uterus.