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