It might seem like an old wives' tale, but breastfeeding really does lower your chances of pregnancy. It does not PREVENT pregnancy though, so take precautiouns unless you wish to be pregnant again.

When a woman is breastfeeding, her body is releasing hormones. This depresses the woman's ovulation cycle, sometimes even preventing ovulations. The more the baby breastfeeds, the more the cycle is disrupted.

Still, no small disruptions are 100% certain. So if your aim is not to get pregnant again for a while, be sure you use appropriate contraceptives!