Prolactin and cycle. When you breast feed, the hormone prolactin is secreted by the pituitary glad to aid in milk let down for the baby. Prolactin causes the secretion of fsh and lh by the pituitary to be suppressed, so the ovaries may respond with no or irregular cycles. You may begin to ovulate and cycle by 6 to 9 months postpartum, so some people get pregnant breast feeding. Hope this helps!
Hormomes. When you breast feed, it changes the hormones in your body and makes you either less fertile or unable to get pregnant. Usually your periods are not regular and you are not ovulating.