I think we're missing one very important piece of advice here, girls. The most serious thing that can happen to you with unprotected sex, no it's not pregnancy!, is sexually transmitted disease. Every single time you exchange sexual body fluid with someone (through intercourse or oral sex) you are risking your life. Think about this and think about it hard, please.
Ask yourself one very important question as well. Are you, at the age of 13 (or 14, 16, 18, even 25) ready to make decisions that will affect you for the rest of your natural life? Also, are you ready to make decisions that will affect another person (your boyfriend, your parents, your future child/children) for the rest of their life? I'm 32 and even i'm not sure I like to answer that question. Everything I do in my life has the potential to affect the ones I love, including the children I have now and the ones I intend to have.
Just some food for thought ... I'll be happy to email/chat with anyone who is interested in talking further. Believe me, i'm not preaching and i'm not judging. I found myself pregnant at 17 years old so I understand what you are going through, believe me.
Take care - momindallas