Breast tenderness can occur after pregnancy, but it usually occurs in the early stages of pregnancy and does not last throughout pregnancy. This is due to the fact that in early pregnancy, the level of estrogen and progesterone increases, and a large amount of estrogen and progesterone stimulates the development of mammary ducts and alveoli, while some other hormones, such as pituitary prolactin or placental lactogen, also promote the development of the mammary glands, so that the breasts will gradually increase in size and become engorged with blood, which will lead to the feeling of breast swelling and pain. In addition, the nipples will also increase in size and darken after pregnancy, all in preparation for future lactation. However, if your breasts remain swollen and painful throughout pregnancy, it is advisable to go to the hospital for a checkup, except for some diseases of the breast.