Many girls will notice that their breasts feel larger right around a week or so before their period is due, while others don’t seem to notice at all. This is all normal. Breast tenderness and swelling happen because of the rise in hormones: estrogen and progesterone. The estrogen that your body makes peaks just before the middle of your cycle. This increase in estrogen causes the breast ducts to enlarge. Progesterone peaks about a week before your period is due which causes the “breast lobules” (milk glands) to grow. Your breasts will likely feel better once your period arrives because the hormone levels decrease. It may be helpful to wear a well-fitting bra to bed (for support) when your breasts “hurt.”