?????

I had my period on the 1-3 of the month, I had to take plan B on the 4th because my fiance and I were having sex and the condom broke, today I was going to the bathroom and there was some light red when I wiped?? I've had to take plan B in the past and this has never happened, does anyone know what it would be?? I'm kind of freaking out, I have a 4 month old and I don't want another kid