Frightened/anxious

can you get pregnant if your man cums on your stomach in the shower and some drips down to your vagina?? i took a pregnancy test a week after (it was negative) and my period came four days early and lasted 5-6 days. This happened on oct 22. I don't know why but I'm still freaked out i could be pregnant. I started taking birth control pills so my hormones have been crazy. Could I still be pregnant?