This could be related to the hormonal fluctuation with respect to your menstrual cycle.When you do your SBE (Self Breast Exam) have you noticed anything abnormal like a breast lump, skin changes or nipple discharge?
Pain in one or both breasts can be due to many benign causes,(including pregnancy) and it's rarely associated with breast cancer.Cysts,breast infection,oral contraceptive pills,injury to a muscle,tight clothing, Costochondritis (which is an inflammation of the cartilage that connects a rib to the breast bone),could cause similar pain.
You could try warm compresses and gentle breast massage.Wearing a good supportive bra, avoiding foods and beverages containing caffeine, such as coffee, tea, chocolate soft drinks and limiting your salt intake, can decrease water retention and may help alleviate the discomfort.
If the pain still persists, you should see your doctor for a detailed clinical examination,including a Mammogram/Ultrasound to find out exactly the cause of your breast pain okay?.
Best wishes and I hope you have nothing to worry about!