My girlfriend is 21 years old and she is having breast pain?

Doctor can examine: A doctor can evaluate a 21 year-old woman with breast pain to see if it is related to trauma, cysts, hormonal changes (menstrual cycle, birth control pills, pregnancy), shingles (chickenpox virus), cancer, etc... Breast cancer is uncommon in young women, but it happens to a some unlucky women every year.

Breast pain: In the abscence of any masses or nipple discharge, the most common cause of breast pain is fibrocystic disease of the breast. Completely benign condition where the pain is cyclic and hormonally dependant.