Post period sex

How likely is it to get pregnant the day after your period? My boyfriend and I had unprotected sex and he pulled out but we did this a few times, so I was wondering if the fact that he had already ejaculated each time if there is a possibility that sperm was in his pre-cum? It wasn't unprotected the entire time just for a little by then he would put a condom on and we would go longer and he'd finish like that