What Causes Pain On The Left Side Below The Heart?

hello..this is about my father. he is 54 years old. he is having so much pain on left side below his heart.that pain radiates in straight line from below heart to till back.he also coughs.he don't like to eat food.he is diabetic. we checked him up with many doctors but no one could cure him.its been 4 months now. we took his x-rays and ct-scans too but it shows nothing.can anyone please explain what could be reason and what should we do about it?