It depends on how long after you ovulated that you had sex. The egg is only viable 12-24 hours after ovulating. If you had sex a day or two before ovulation, then it is possible to get pregnant because sperm can live in the body for a few days. The sore nipples/breasts can certainly be a early sign of pregnancy, but it also can mean impending period. Mine always get sore 1-2 weeks before my period starts. If your test said negative, then it's more than likely accurate. If your period still hasn't started in the next week, I suggest you go see your Dr about it.
~Jenn~ Mom to Ethan - my heart surgery survivor - born 6/29/09