The possible causes are:
Acid reflux : this seems the most likely cause. Such pains can be associated with lying down and are usually more at night..
Chronic cholecystitis : the pain is usually associated with indigestion, flatulence and often with fever and vomiting. A pain from the gall bladder may be aggravated by deep breathing or lying down as the diaphragm touches the gall bladder.
Pleurisy : An inflammation of the lining of the lungs. This is a likely cause but it is usually associated with some sort of cough and often sputum. Without this, it is less likely.
Costochondritis: If the pain is aggravated by touching, it could be due to costochondritis, an inflammation of the cartilage joint of the ribs.
Esophageal spasm: may be associated with difficulty in swallowing and heart burn. link
Cardiac causes: Cardiac causes of such pain could be due to ischemia (due to blockages - including both stable and unstable angina and acute heart attack and coronary artery spasm), pericarditis (inflammation of the sack around the heart), myocarditis (inflammation of the heart)
Psychological causes of chest pain are common and include panic attacks, anxiety, stress and mental duress
For you, acid reflux is the most likely cause. You should try initially with some antacid, like Mucaine gel (OTC) 2 tsf three times daily and Tab. Zantac 150 mg once daily assuming it to be acid reflux. If this does not help and pain continues more than 5 days, then you have to go for a medical check up. Link1 Link2
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