It's normal for your breasts to swell for up to two to five days after you give birth (this is called engorgement). It happens because your body is figuring out how much milk you need to produce and when, and this can make your breasts swell or feel rock-hard. Most women can tell when their milk comes in -- your breasts might feel like foreign objects attached to your body.
To prevent pain, wear a supportive bra, both during the day and at night. Also, nurse your baby on demand, apply cold cabbage leaves (their shape can conform to your breasts); and when necessary, pump out excess milk. For moms who opt not to breastfeed, avoid any nipple or breast stimulation. And to help constrict your breasts, apply cold compresses, which help stunt milk production, and wear a sports bra. --Allison Winn Scotch