Reasons for a missed period?

Courtney
Hey guys, this month my period was 4 days late. I'm obviously not pregnant as I have my period now but I just want some reasons for this? I'm not overweight or anorexic either, I would say I'm about right. I haven't been too stressed lately, so I'm really not sure why my period was a little late. It is usually VERY regular. Thank you. ☺️