If a woman’s breasts are swollen and painful after menstruation, but the amount of menstruation is normal and pregnancy is ruled out, it may be caused by organic diseases of the breasts, such as the most common mastocytosis, which requires a visit to a hospital gynecologist or mammographer for a mammogram to confirm the specific problem. If a woman has an abnormally low menstrual flow, has intercourse without contraception, and experiences constant breast swelling and pain it may be a sign of pregnancy and is not really menstruation, but abnormal vaginal bleeding due to pregnancy. You need to go to the hospital for a blood HCG test and ultrasound to confirm the exact cause.