Missed period, but negative pregnancy tests

Hi all, I hope I’m posting this in the right place. My husband and I haven’t started actively TTC yet, but I’ve been off my BC for a couple months (have started ovulating again and gotten a period). I have been tracking my ovulation through the app and ovulation tests. I ovulated on 9/06 and was supposed to get my period on 9/20. I’m now on my 4th day late, not so much as a spot. I took a pregnancy test on 9/20 and 2 different brand pregnancy tests today, all unambiguously negative. Is this normal???? These pregnancy tests are supposed to be able to tell you before your missed period, so it couldn’t be that I’m taking them too early right?