Late/negative result. AVOIDING pregnancy

Okay. I don’t post much at all. But. I really need some help. My period is somewhere between 3 and 5 days late. (I’m horrible with tracking my period 🤦🏼‍♀️) I have no clue when I ovulated. I typically have a regular period. I’ve never been this late before except with my two girls. But with both pregnancies I was able to take a test by the 3rd day of my missed period and tell whether or not I was pregnant. Stress has gotten to me and I’ve decided that I don’t want anymore children. (Sorry for rambling) what are some reasons I could be late?