I don't know the father of my baby is, am I counting wrong?

I have a problem here I slept with my boy friend while I was still menstruating on the 23rd of November 2014 and after my period was off on the 26th of november 2014 I slept with my ex boyfriend I find out yesterday that I am 9weeks and 5days pregnent and I don't know who the father is and when am counting I got that the father is my boyfriend