Fertility Postpartum

Today a friend of mine told me that she is pregnant with baby #2 after just giving birth to baby #1 in May! Three months seems such a short time anyways, but here's the crazy part. She said they were using birth control AND condoms plus I know she breastfeeds. What in the world?! Lol. Is this level of fertility normal after having a baby? Apparently, condoms can't be trusted. But birth control is like 99% effective!