Just started BC

Pari • Mom to a beautiful former 28 weeker!

I had my baby in Feb 2016 preterm @ 28w 2days, got my period back in May, had regular period until my milk supply dropped in October, when it became irregular until April when I stopped pumping and I haven't had one since. My doctor put me on birth control and I just started it. I am HIGHLY against BC but no other option to regulate my cycle. How long does it usually take to regulate your cycle? I want to get off of it ASAP