Pregnant while exclusively breastfeeding?

My baby is 4 months old and exclusively breastfed. He won't take a bottle or a pacifier. My husband and I have sex a least 2xs a week but I haven't started birth control yet. I was really sick when I was pregnant and today I was so nauseous and dizzy. I read it's nearly impossible to get pregnant while EBF if you nurse right. I've read all the rules to using it as birth control and my husband pulls out (usually). My question is how many of you have gotten pregnant while ONLY breastfeeding. No pumping or anything.. I'm  kind of freaking out!