Breast tenderness before menstruation is very common and is usually caused by hormonal changes. Why it happens: 1. Hormonal fluctuations Changes in estrogen and progesterone before your period can affect breast tissue. 2. Fluid retention Hormones may cause the breasts to hold more fluid, making them feel swollen or heavy. 3. Increased sensitivity The breasts may become more sensitive to touch during the days leading up to your period. You may notice: • soreness or aching • heaviness • swelling •