Hi, Flucloxacillin is a type of antibiotic that is commonly used to treat bacterial infections. While it is unlikely that flucloxacillin would directly affect your menstrual cycle, it is possible that the infection it is being used to treat could be impacting your cycle. In general, antibiotics are not known to directly affect menstrual cycles. However, certain infections or illnesses that require antibiotic treatment can impact menstrual cycles. For example, a severe bacterial infection can cause stress on the body, which may result in irregular periods or missed periods. It s also possible that the morning-after pill you took could have affected your menstrual cycle. Emergency contraception can sometimes cause changes to the menstrual cycle, including earlier or later periods, heavier or lighter bleeding, or skipped periods. It s important to note that many factors can affect menstrual cycles, including stress, changes in weight, and other medications. If you are concerned about a missed period or changes to your menstrual cycle, it s a good idea to speak with your healthcare provider. They can help determine the cause and recommend appropriate treatment if necessary. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician