The bottom of my left breast hurts and it been going on for a week. i was wondering what it could be. the right one doesn't hur at all. ?

Multiple options: Breast tenderness can be due to trauma to that area, a bra not fitting correctly, fibrocystic breast tissue, if other benign breast masses. See doctor for evaluation. Use ice pack, ibuprofen, and decrease caffeine to help with tenderness.

Exam: Need exam by a Breast specialist usually a general surgeon to evaluate

Fibrous mastopathy: Pain in breast is essentially never associated with cancer. The latter, which is related to a mass in the breast , does not initiate any symptom when palpated other than for diagnosing its presence. Pain is due to a somewhat distended milk duct which has not emptied the typical fluid produced, and is part of what is called cystic mastopathy which is benign unless defined otherwise by a mammo