If you only just started your period eight or nine months ago, your body could still be trying to find a normal rhythm. There can be irregularities at first. However, if you have this happen again next month, go to the doctor. Like Ash said, you can be put on birth control to regulate it if it becomes necessary.
It happens sometimes. Might bring it up to your doctor and if it gets all out of whack again they can put you on birth control to regulate it