Assuming you were on the pill for a long time your period will tend to be spotty for awhile. While your body weans itself off the dosage it is not uncommon to not have a thirty day cycle. Make sure you use another form of birth control.
When you stop taking birth control pills your might not have a period right away. This happens quit often because your body needs to adjust from being off the pill.
You can expect that your period may or may not come on time or for a few months. Once it does come it may be a little heavy and you might have some cramps. They could continue to be irregular for a few months after you come off of the pill. You may also experience light spotting.