Period after starting bc

Monica • Married & Pregnant w/#2

So I had my son 4 months ago and finally decided to start taking my pill this month. Well I’m going on day 16 of my period.. has this happened to anyone else? (Btw the flow has been up and down.) Also my first period after pregnancy was 8 weeks after delivery and all of them before taking bc have been the normal 4-5 day cycle