Breast Pain

For the past three months now I seem to have left breast pain associated witha lump about a week before my period. My other breast is tender but not at all as sore as the left, and usually resolves itself when period ends. I am a healthy 26 year old female who has not had any problems before. I understand this is very common but I thought that it was both breasts and its only one....

[Cleveland Clinic]

Dear kb720, Breast pain is a common breast symptom.  The reason for breast pain is not clearly understood, and is not usually associated with breast cancer.  Breast pain is sometimes associated with hormonal variations and is then called cyclical breast pain.  Noncyclical breast pain does not seem to be linked to hormonal variations and is often localized to one area of the breast tissue.  Noncyclical breast pain may or may not be the result of an injury to the breast.  Breast pain does not necessarily have to be restricted to one breast.  
You also mention a lump.  Does this also come and go with your periods?  If not or your symptoms continue to be of concern to you, you may want to have this checked out by your doctor, they would be better able to evaluate being able to examine and discuss.