Whether you're breastfeeding or not, your breasts started undergoing changes as soon as your baby was born (as if they haven't changed enough during your pregnancy!). The instant you pushed out the placenta, the process of milk production was initiated (It's what your breasts are designed to do naturally!). At that point, it was out with the old (hormones), estrogen and progesterone, which declined dramatically, and in with the new (hormone), prolactin, which is in charge of activating the milk-producing cells of your breasts. And with activation, your postpartum breasts started growing even bigger than they were during pregnancy (and to proportions you thought only a plastic surgeon could approximate).
