Pain under the left shoulder blade is usually a referred pain from abdomen like
stomach ulcers, pancreatitis,
or ectopic pregnancy
or from the chest like in heart attack, pericarditis, pleuritis, pneumonia, pulmonary embolus, and aortic dissection. Pain under right shoulder blade is usually due to gall stones, duodenal ulcer and liver infection. Hence an ultrasound, liver function test and an upper GI endoscopy is needed for diagnosis. Liver infection can also cause fatigue and bruising.