Can I-Pill Affect Periods?

hi doctor. i had unprotected sex with my bf last month during the menstrual cycle (on the 3rd, 4th and 6th day ) but each time i had an i-pill to make sure i dont become pregnant. this was during 14th to 18th nov 2010. i again had periods on 26th nov or so but now m worried because i should have got my periods by now which i havent. m planning to take strip pregnancy test. whya do u think my periods are delayed ? is it because of the pill?