It all depends on your hormones.. that, and whether you're a virgin or not. Even the slightest change in your stress level, diet, ect., can effect your period. It's so annoying.
If you're a virgin and you've used protection, you shouldn't worry too much- condoms do work. Also remember that your period has a complete mind of it's own (though that can be very frustrating.)
As for tampons, if you want to start using them, please start out with the small size and stay away from the cardboard ones, they hurt!