Birth Control pill question?

i know that when you're on the pill, the last week, sometiem, any time in that week you can get your period.. how oftern does it normally happen towards the end of the sugar pill week? cause i am used to mine starting midway, and it hasnt yet.. yes, i am sure there is a possability i could be pg, which wouldnt be so bad either, but i am curious.. do a lot of people get their period later rather than sooner? and whats the earliest i can take a pg test?