Condom Broke!

Soo, I had sex with a guy today and he used a condom. When he nutted the condom broke inside. I ended my period yesterday so my question is, am I most likely to get pregnant still because most people say you are highly fertile right after your period but if that's the case then an incident like this that has happened to me before, I would have gotten pregnant then but I didn't?? And how affective is the Plan B pill?