What Could Cause A Week’s Delay In Menstrual Bleeding While Being Sexually Active?

Hi um so on the 28 oh july i had sex but on the 2 of August i thought i started my period but it was only for one day and it was kinda light and not normal looking compared to my period but then on the 11 my period came but then this month I m 8 days or so late on all 3 of my period calendars and I ve never been this late before, and anyine tell me if this is normal or if somethings wrong