What would cause an on and off pain on the right side of my chest, inside my pectoral muscle? negative echo, ekg, holter monitor, and stress test.

Muscular: Your pain is most likely musculoskeletal, with other possibilities still open, lung and gi related, for example. Keep monitoring your pain with circumstances around it and keep a log. Then, see your doc for a review and exam and take the log with you.

Agree with Dr. P: It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor and discuss if you may be depressed. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated. Wish you good health!