Dear Jenny it may be the side effect of contraceptive pill/postinor. It is an emergency pill that is taken within 72 hours of unsafe sex, the sooner it is better to sleep, but it can affect a woman's menstrual cycle. Please don't use these pills carelessly, condoms are used for safe sex and not emergency pills. As you said pregnancy test is negative so it's better to consult a specialist or a registered doctor. Please use a condom from today onward. Read this write-up: https://lovematters.in/en/birth-control/chosing-the-right-birth-control/morning-after-pills-instead-of-condoms-is-that-ok If you would like to join in on a further discussion on this topic, join our discussion board, "Just Ask” https://lovematters.in/en/forum