How old are you? Is there any possibility that you are pregnant? Is it affecting one or both breasts? I would see your doctor is there is any discharge or lumps.

Some degree of breast tenderness is normal. The discomfort may be caused by hormonal changes due to:

Menstruation
Pregnancy -- breast tenderness tends to be more common during the first trimester and in women who are pregnant at a young age
Puberty -- in both girls and boys
Breast feeding
Approach of menopause -- once your menstrual periods have stopped completely, breast tenderness often goes away unless you are taking hormone replacement therapy

Fibrocystic breast tissue is common. Such tissue contains breast lumps and bumps that tend to be more tender just before your menstrual period.

Certain medications may also cause breast pain, including digitalis preparations, aldomet, aldactone. certain diuretics, anadrol, and chlorpromazine