Every women gets it at a different time, but it's normally a month.
If this is your first year having your period then it will be irregular.
But after a year or so, it will be at least every month.
But if you've been having your period a while
then you probably should see a doctor. =)
Either you have seriously painfull ones that when its over, so much blood has come out that there is no other period for a month or ur a beginner were it gets more recent through tine
ask your doctor about provera and birth control pills can help regulate it