So i've got this sharp stabbing pains in my left side under my breast,can feel it when i breathe. what can it be?

Chest pain: Such chest pains on a deep breath can be caused by a pinched rib cage nerve, rib cage injury or strain, pleurisy or pneumonia, pulmonary embolism, or pneumothorax. Associated cough, shortness of breath or fever would suggest a lung problem. Pinched nerve usually resolves in a few days. See your physician if not improved or if symptoms worsen.