On my rib underneath my breast theres a slight bruise and i've had it for a long time now not much pain just a little discomfort what could it be?

Hemangioma/hematoma: It depends on how long you had the "bruise" for: if few weeks or few months it may be a hematoma (blood that leaked from ruptured vessels due to trauma or bruising) and should clear shortly but if you had for years or since birth it can be a vascular anomaly or hemangioma (benign tumor of blood vessels). If it blanches (turns pale) whem you press it, it is likely a hemangioma