Hi My Partner Nd I Had Unprotected Sex Last Apr

Hi my partner nd i had unprotected sex last apr 27 around 11pm. He did not cum inside me but im afraid of pre cum so i took nordette ecp apr28 around 11am 1st 4pills and 11pm 2nd dose of ecp. Last menstrual period was apr16. But it has been 13 days and still no withdrawal bleeding. I dont feel any side effects since this is my 3rd tym taking nordette as ecp. I took my 1st nordette ecp last 2014 and 2nd nordette ecp last yr. can no withdrawal bleeding mean nordette lost its effectivity or what? Pls help