I have been on trinessa for a whole month and when i finished the pack i made a switch to loestrin24fe. On the fourth day of being on loestrin24fe i had unprotected sex. what are my chances of becoming pregnant? I've been reading that when making a switch from a different brand of contraceptive pills that there is a seven day rule of starting the new birth control pills, to avoid getting pregnant. How much of that is true?