What Causes Irregular Menstral Bleeding And Sharp Pain In The Rectum During Menstruation?

I am 30yr old momma of 3 and my period has become painful. It hurts if I have gas or need to make a bowel movement the day before my period starts and during the first day or so of my period. It feels like a sharp pain in my rectum. My period also stops after starting for a couple of days and then it starts again a day or so later and last a few more days.