I would see a doctor but I know that changes in weight can influence periods. Have you gained/lost weight recently, as this could change your cycle? A few years ago I was struggling with my weight and lost a considerable amount of weight in a short period of time. For years after, in fact until I started on the contraceptive pill, my periods were strange...I could go 9 months with no period and then have one that lasted like 2 days. So maybe this could be a reason? Like everyone else suggested though, I'd get in contact with your doctor to be safe.
Hope this helps
