could I be pregnant?

If my boyfriend and I had anal sex the 3rd day of my period and possible precum came in contact with my vulva/vaginal opening/clit what are the chances of me becoming pregnant? He never penetrated my vagina..we have never had vaginal sex just anal. I have a 28-30ish day cycle and week long periods. I was wearing a Fallon when we were screwing around as well and no actual ejacualtion came in contact with my vagina just possible precum. Could it live inside of me until I ovulate?