Crazy periods

Has anyone else been having really strange periods lately? I started paying more attention to my menstrual cycle back in August-September, well it was lasting about 5 days with medium flow, now last month it was really heavy with clots and lasted only 3 days, now this month it was like medium-light and lasted about 48 hours, so strange. Not sure why this is happening and the last test I took was like a week or so ago and it was negative.