I am experiencing pain on the left side of my rib cage right under my left breast, so far it hasn't stopped for two days, I haven't done anything physical in order to pull a muscle, what should I do?

Be seen. Many potential causes, I would encourage you to be seen for a specific diagnosis. Potential causes could include a thoracic radiculopathy from a pinched nerve in the spine to pleurisy, pancreatitis, costochondritis, among many other possibilities.
Pain . You may have a pleurisy or inflammation of the covering of the lungs. With pain that is unremitting I think you should see a physician and get a definitive diagnosis .