Hi! I can understand your concern for the efficacy of oral contraceptive Femilon Femilon is a combined oral hormonal contraceptive pill containing Estrogen & Progestin that works by preventing ovulation (the release of a mature egg) and may also alter the mucus in the cervix to stop the sperm from entering. There are 3 ways to start taking the pill with the guidance of a qualified health personnel. 1. The easiest one, pill is taken on the first day of the menstrual cycle. This way, protection from pregnancy starts right away. 2. You can start anytime within the first 7 days after you start your menstrual period. This method is best combined with a back up method of birth control such as condoms and spermicide during the first 7 days of use. 3. The pill can be taken anytime during the cycle, as long as you are sure you are not pregnant. Protection starts after 7 days of taking them and all through out the cycle if taken correctly and continuously. So, since you have taken Femelon on 7th day of your menstrual cycle (11th May) instead of the 1st day (5th May), the pill will not be effective for another 7 days. In view of the unprotected sex on 16th you are not protected against pregnancy, so you will have to take a post coital emergency contraceptive pill like I pill to prevent the pregnancy. Hope this answers your query. A feed back is appreciated.