Lots of things can make your periods go screwy. It can be some kind of hormonal imbalance. Stress can be a doozy on your cycle as well. If you're really worried about this, seeing a doctor would be a very good idea.

I've had this happen to me before. For two months I had periods every two weeks.

My cycle is quite irregular due to eating disorder crap.

I hope you find answers and feel better soon.