I feel a painful lump under my breast on my left rib, by my bra line. it isn't a superficial it is deeper in the skin and very tender to the touch. it is also causing rib pain. i had a negative mammagrophy and ultrasound. also ekg normal. cyst?

Not a cyst. Skin: If the ultrasound didn’t show a cyst, it would be hard for a cyst to be present. The ultrasound is very good at detecting fluid-filled structures. I suspect something injured or bruised the rib which wouldn’t be seen on any of the x-rays or tests that you’ve had. Have you been in a car accident (Seat belt)? Do you play sports? Wear underwire bras? The simple explanations are most often correct.

Need exam: An exam will probably allow a definition of your problem. Your description permits only this advise.