Feeling like not getting enough air. Constant bleching, pain under ribcage and sore shoulder. Left leg pain too. Normal ekg.

Stomach vs lungs . Sounds like a gastric issue to me, maybe even irritable bowel (but less likely). Another possibility is a pulmonary embolism, a blood clot going to the lung. That usually manifests as pain with breathing (pleurisy), shortness of breath, even sometimes coughing up blood. Most often happens after being laid up in bed, driving long distances, or taking long airline flights. If this the case get to ER.
See your doctor. This may be something simple such as Flu or even a pneumonia. Please see your doctor.