Hi, Thanks for posting in HCM. I understand your concern. Microgestin Fe 1/20 is a combined birth control pill, used to prevent pregnancy. It contains 2 hormones: norethindrone (a progestin) and ethinyl estradiol (an estrogen). Your pill pack contains 21 pills with active medication plus 7 reminder pills with iron. Take one active pill (with hormones) once daily for 21 days in a row. Take one inactive pill (with iron) once daily for 7 days in a row after you have taken the last active pill. You should have your period during the fourth week of the pack. After you have taken the last iron tablet in the pack, start a new pack the next day whether or not you have your period. While taking it for the first time, you need to take 1st pill on the first day of your menstrual period. For the first cycle of use only, use an additional form of non-hormonal birth control measures such as condoms and spermicidal agents, at least for the first 7 days to prevent pregnancy until the medication has enough time to work. In your case, it should be fine and the pill should have started its action as you had unprotected intercourse during 3rd week. In case you do not get your periods in time, kindly take a urine pregnancy test and seek medical attention, as you have not started the pill on the first day of your period. Hope the information provided would be helpful. All the best.