uterine lining?

I'm on the placebo week of the first month, I had been lightly spotting a few days before the placebo week. On day 3 of the placebo week (yesterday), I started my period. It's been about a month that I've had my period because I started the pack before my period, causing it to delay. 
Anyway! This giant white thing came out, which never came out of me before. I'm just wondering if this has happened to anyone else while starting the pill?