Hi,
Thanks for the query.
Since you have used Birth control pills irregularly and also used
plan B, it is difficult to predict when you will have a period. Even with this, in most cases, for women using birth control pills, periods will come only after the active pills are over despite using plan B in the middle of the cycle.
Plan B works in more than 90% cases if taken properly. Concomitant use of both does not decrease the efficacy of plan B and it still works. It works by delaying ovulation and changing the lining of the
uterus to prevent
pregnancy from occurring. It does not work if pregnancy has already occurred.
The best way to know if you are pregnant in this case would be to take a pregnancy test at least 3-3 1/2 week after using plan B using a morning urine sample. If it is negative, chances of pregnancy resulting from the sexual act on that day [before you took plan B] are negligible.
Another way to know is wait for your period while taking the sugar pills, if it is delayed a pregnancy test 7 days after the missed period will help.
Hope you find this useful.
Thanks for using HCM, and have a good day.
Dr Madhuri Bagde
Consultant Obstetrician and Gynecologist