Hello Amrin, Ipill provides contraception by preventing the fertilized egg from traveling down the fallopian tube and implanting in the uterus. However, as these pills contain high dose of hormones, they interfere with the regular cycles & cause delay in the subsequent cycle. In case of pregnancy, the tests usually comes positive within the 1st week. So, if you have calculated the dates properly(considering that February had only 28 days), presence of 4 negative tests rule out pregnancy. So, it will be better to consult a Gynecologist & get a proper examination done to rule out any other cause for delay in periods. So that appropriate management steps could be taken. Wishing you a Good Health. Thanks & take care