Morning after pill

I had unprotected sex while I was on my period and then to be sure I took a morning after pill the next day. I've been feeling really nauseous and dizzy and lots of stomach cramps since then, but put it down to side affects of the pill. Today I found a weird clot type thing (have also been havinh lots of grainy brown discharge) when I looked it up it said it could be a miscarriage, but is that even possible? I know that the morning after pill isn't 100% effective but I didn't think there was such a high risk being on my period. Thanks!