How soon do you have a missed period when you become pregnant?

Today my boyfriend and I had unprotected sex. However, he pulled out and jacked off until he ejaculated so that he would not ejaculate inside of me. I'm on birth control and my period is due to come on Monday...it's Friday obviously. If I would end up pregnant...would I miss my period next week? Or is it too soon for me to miss my period? Thank you for the answers. I appreciate it.