They do diagnose pnemonia with a xray but to see a blood clot would require a cat scan, and to see a blockage would need a echocardiogram
which is a ultrasound
of your heart. Excessive coughing could cause pressure in your chest. See a cardiologist to be safe, and its important that all your doctors know your family history of heart problems. If it doesnt go away go back to the ER.