Period

Hey girlie, I just need y’all’s opinions. The last time I had sex was December 26 and it was with no condom. I just started using this app and it’s telling me I’m 3 days late. The app that I was using for a good two years is telling me I don’t start until next week. I did take a pregnancy test because I am a very paranoid person and it did come out negative, but do we really think that that is accurate  ?????? Please help