Best options?

So my period ended on Friday officially and today I was going to start my birth control pills since it was Sunday. I have a very normal and regular cycle. I also had unprotected sex today. Dumb I know. We had sex twice and while he pulled out both times you never can be extremely sure. I'm not extremely worried but I wanted some feedback. I was wondering if I should just go ahead and start my birth control and since it's pretty soon after my period I shouldn't have released an egg yet? Or should I go get some Plan B tomorrow at the store? I don't want to get Plan B if I don't have to since I've heard of some of the horrible side effects. Any feedback?