Help!! 6days late!

Hey all.

I'm 6days late my periods have always been on time like to the day on the app.

I took a one test 2days late it was negative and one today 6days late and it's also negative. I don't understand why my period is late and the tests are negative. I had unprotected sex with my husband like 1week after my period so I thought I was pregnant I just want confirmation I feel a bit lost. Any reasons I could have a missed period? I'm not stressed out or anything.