If you BD'ed before and after ovulation, chances are it was the sperm that was there before you ovulated that got you pregnant. although, nothing is impossible.
The egg usually only lives between 12-24 hrs once it is released. Sperm must me there to meet it withing that time or it will die. Sperm can live in fertile cm for up to 5 days b4 ovulation. Conception happens once they meet, implantation happens usually 6-10 days later.