Pains in lower stomach, periods late, brown discharge and bowel movements allover the place

My periods were due 1 week ago, i had 1 day where i had servere stomach pains and a small amount of dark brown discharge with clear discharge, the smell was bad, then it went away. A few days later i thought i was getting my period instead i've been getting discharge that is a dark brown colour and has been on and off for approx 5 days, with bowel movements that range from constipation do diareah, What would cause this and what should i do?