My periods have always been super regular for about 4 1/2 years. Always get it on time. But last two or three periods (Nov and Dec cycles) were both late by a week or more. Also very painful with cramps. I started getting brown discharge off/on two days ago and today it turned to blood so I guess my period is here. I already had a period Dec 4-8th. What could be suddenly causing all this irregularity? I am not sexually active, and haven't been under any new stress, haven't gained or lost weight.