What Causes Pain Under The Breast Radiating To The Armpit?

I am 42 and i am having a real bad pain under the left breast moving up to the side by the armpit . It hurts really bad and it has been hurting for a while .i did all tie medical test like mammography, ultrasound,X-ray, blood test and all test are normal of Can anyone help me with suggestions and also what may this be or could be .

Thank you