What Causes Delayed Period After Taking Primolut N?

Hi,

i expected my period on the 30th December 2010. Was goin abroad on vacation so i didnt want a period i took Primolut n from the 28th and stopped on the 31st December but i had unprotected sex on 26th and now i still havent gotten my period am i pregnant or was pregnant before i started taking Primolut n or it just has'nt come as yet .......please help



Thanks

S.D