You may start the combination birth control pill at any time. If you start within five days after the first day of your period, you are protected against pregnancy right away. For example, if your period starts on Monday afternoon, you can start the pill up to Friday afternoon to be protected from pregnancy right away. If you are later than 5 days after the FIRST day of your period, you will be protected from pregnancy after seven days of taking the pill every day. Use a back-up method of birth control like a condom, female condom, diaphragm, or sponge — if you have vaginal intercourse during the first week of starting the pill. Also, the pill does NOT protect against STDs, so always use a condom WITH your birth control if you want to avoid getting STDs. To know more about the pill check out this post.