When taking birth control, when do you start your period?

I am almost 25 years old and have never taken birth control before. I just started taking it 4 days ago to regulate my cycles. Since I've never taken it before, I had no idea when you would actually get your period. I am taking it for Polycystic Ovarian Syndrome.When taking birth control, when do you start your period?
It can be different for most women. I have been on birth control for almost five years now. I always take my placebo on a Sunday (becuase I am a Sunday start) and I normally get my period on either Tuesday evening or mid day Wednesday. I hope this helps!
My partner tells me she has her period 4 days after she has her last pill.