Just recovering from a flu. what is causing a sharp pain under the right breast whenever i breathe or cough? also coughs up phlegm w blood 2x now.

Pulled muscle likely: To sort this out completely would require a physical examination, but you probably injured your rib cage in some way during a coughing spell. Such injuries are not rare and usually heal on their own, in time. An inflammation on the outer lining of the lung (pleurisy) is another possibility. The bloody phlegm is a concern. It may simply be due to bronchitis, but have your doctor check it out.