Sex incident question

Kierstin • Nanny: jack of all trades, master of none
So the other day my boyfriend and I had sex just like normal and when he pulled out there was blood. It wasn't a lot but I'm on the patch and still have a week before I take it off to have my period. I was one day late switching my patch but normally it takes several days without a patch entirely before my period starts. Any ideas? Is it common? I asked several girl friends and they all suggested calling my gynocologist...