Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Emergency contraceptive pills such as Postinor are specific drugs. It proved to be quite effective and safe in avoiding unwanted pregnancies. However, if used improperly, the drug can cause side effects such as nausea, vomiting, menorrhagia, etcetera. This pill has the effect of inhibiting ovulation in a woman. In case of loss and egg is fertilized, the drug would alter the endometrium to prevent this nest egg. Thus, if a fertilized egg has the nest, the drug is ineffective. In other words, this medicine for abortion does not work as some people think, and should not be taken when pregnant. Your cycle may change. Your ovulation can be predicted wrong and nest egg in the uterus. Meanwhile, the drug had no effect, and you can still become pregnant. So after a week, I recommend that you should check to make sure the pregnancy test stick more. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Chung Luu