What Causes A Delayed Menstrual Period After Taking Postinor 2 ?

hi! I had unprotected sex last week on 6th and took postinor 2 on 7th morning, I did a blood test yesterday but I wasn t pregnant, is it too soon, and can the postinor 2 fail. my periods are due this week but I have no signs at all, am on other medications too coz I was found with very little blood. could the meds am on be giving me an irregular period, and I was also found with protein in my urine. pliz help me understand all this.