Period 4 days late

My period is usually always on time every month except this month. Had unprotected sex March 11th (app said I ovulated March 1 and so the 11th was my safe time) and period was supposed to be due within the next 6days. It’s day 4 and still nothing. Should I take a test? Should I wait 4 more days to see? Any thoughts on why my period could be late?