Breastfeeding is as effective as contraception as a photo of the pope over your bed. My lovely cousin came to being while his older sister was only 3 months old.... on the breast, and still no periods. The body might not create the lining for the egg, release the egg, get rid of the lining etc.... but might not doesn't mean will not. 3 ladies in my BF group are preggers again so we just got this lecture from the nice midwife that runs it.