Pieces Falling Out of My Vagina

So according to Glow I'm supposed to start my period in two days and I'm thinking this has something to do with it, I'm just curious if anyone has experience with their uterine lining or any piece of them falling out after sex? It was rough, and the pieces are pink and look sort of like large eraser shavings. Should I be worried? I have a couple menstrals issues so I'm not really worried, and my pms symptoms are mostly normal.