I have a period question!

Hey guys I have a question!

Me and my boyfriend had sex- 4 days and day of ovulation, both times he finished inside and Im not on any birth control. This past Thursday I was supposed to get my period (3 weeks after my ovulation day) and it’s Saturday night and I have still yet to get it, which is very very odd! I took a test this morning but not with “first morning pee” because I’ve been up and down all night and early morning. The test came back negative but I’m so unsure why I have yet to get my period when I never don’t get it or rarely late- If I am late it’s normally just a day.