If me and my boyfriend have sex at the beginning of the month and my period is at the end of the month and i miss it, is it to late for birth control?

Birth control: It is too late if you are already pregnant. You should do a pregnancy test. If it is negative then consult your doctor about getting birth control if you are not ready to get pregnant now. If you are positive for pregnancy you should consult with OB doctor.

Plan B: The only good option is to get Plan B at the pharmacy to prevent the possibility of an embryo from implanting - this is about 80% effective if taken within 72 hours after intercourse.

Taking Chances!: Let's say you start your period on the 23rd. This means that you're ovulating 2 weeks later on the 7th. You are having sex at the exact time that you are most fertile! Plan B is not a bad idea if you think you're pregnant. The best idea would be to make sure you're not pregnant now, and then get started on a regular, all-the-time birth control method to prevent close calls like this.