I Made Love With My Partner On The 28th Of

I made love with my partner on the 28th of March. I took Postinor 2 almost immediately nd the second dose after 13 hrs thereabout. Am suppose to be on now but am not. That 28th of March was exactly one week after I finished my cycle. I've not seen my flow. Am I pregnant? I am actually not feeling pregnant at all cos I've got 2 children from my past marriage. But why am I not flowing?