The enlarged and swollen breasts are caused by the following reasons: firstly, it may be due to pregnancy, which is due to abnormal levels of estrogen and progesterone, causing the breasts to gradually become larger and swollen in preparation for breastfeeding after delivery. Secondly, it may be due to the imminent onset of menstruation. Most women experience breast enlargement and swelling before menstruation, and sometimes pain, which is a normal physiological phenomenon that will slowly recover after menstruation. It may also be due to the fact that the breasts are developing during puberty, which is a normal developmental phenomenon, or it may be due to breast enlargement or inflammation, if they become bigger and swollen but not accompanied by pain and lumps, most of them are fine.