What causes a short stabbing pain in side of left breast near armpit?some dull pain in ribs below armpit & below bra line of pcp says heart ok.

Costochondritis: Costochondritis, or Tietze's disease results from irritation of the cartilage that joins the upper ribs to the breastbone. Pain is typically manifest with movement, deep breath, cough. It is a benign condition, which can be properly treated with nonsteroidal anti-inflammatory drugs, and osteopathic manipulative medicine. Mechanical irritation due to bra wires can exacerbate the symptoms.