What Causes Delayed Periods With Negative Pregnancy Test Result?

Hello Dr. I am Mona I did sex with my bf on 6th of jan and had i-pill,my periods were due on 1 feb but still they are not coming please help .Please tell is there any chance of pregnancy and if so can i take abortion pill now, did preg-test on 6th feb, it came negative and still i cud get pregnant ?