What's going on: A surge in estrogen and progesterone in early pregnancy, and the milk-making hormone prolactin later on, spurs dramatic changes in your breasts that help them gear up to feed your baby-to-be. Nipples become erect, the areolas around them expand and darken (all the better for a hungry, nearsighted newborn to zero in on), and small milk-producing glands that dot the areolas grow more prominent. Transformation is going on inside, as well: Blood flow to the breasts increases; milk sacs, lobes, ducts, and sinuses grow and multiply; and protective fatty tissue plumps up. As a result, your breasts pack on up to two pounds each -- a cup size or more. (Sorry, this voluptuousness will subside once the baby's weaned). Not surprisingly, breasts also become achingly tender and sore.
What to do about it: If your cups runneth over, invest in a good support bra with wide straps and smooth material that won't irritate hypersensitive nipples. Be sure to have it professionally sized, and sleep in it if you have to.