What Causes A Delayed Menstrual Period And Negative Pregnancy Test?

hello, i took the levonelle pill 2 weeks ago after having unprotected sex, i started getting cramps and feeling sick and suffered with lower back pain. i took a pregnancy test which was negative.. i havent had no bleeding or had my period yet and it was due around the 9th.. im still feeling sick but the test is still coming up as negative, whats going on