Hello,
There are many causes of
soreness of breasts,premenstrual syndrome and pregnancy being one of them.Other important causes are fibrocystic breast disease,ductal ectasia,mastitis(inflammation of breasts),galactoceles,benign and malignant pathologies of breasts,referred pain from liver or musculoskeletal system,arthritis of the ribs,costsochondritis and inflammation or sprain of pectoralis muscle.
I feel that an examination by a gynecologist will be the best.