I'm on the BCP but.?
Answers: I'm not a doctor or anything, but I did abundantly of research before, and after I first started the pill. The BCP is taken the first Sunday after your period starts, even if you're still bleeding. The path the BCP works is by inhibiting your ovaries from releasing eggs, as well as changing the facing of your cervix and your uterus (so that IF you do release one and its fertilized, it probably wont implant.) So, regularity or not, if you took your pill on the first sunday after your period, next you technically havent ovulated this month, and therefore, if youre taking it like you should (not missing) consequently theres little to NO chance of being pregnant. When you DO enjoy your 'period' while on the pill, its not actually your period (IE expelling egg and uterine lining) but more of a pseudo-period. Blood, a small amount of uterine tissue, but zilch more than that, and you only bleed because a drop off within the hormones. Technically, you could skip over the placebo pills and not have a period for 3 months straight, though you would termination up 3 weeks short before your next prescription.
Assuming you wait the 7 days like youre supposed to after taking the pill before have sex (unprotected), and you take the pill at the same time every afternoon (+/- 1 hour) you shouldnt get pregnant..
The birth control pill should help regulate your time so you know when to expect it.