Hello,
One possibility is of gastresophageal reflux disease or hiatal hernia or peptic ulcers.You need upper GI endoscopy to diagnose it.
Thisd possibility is of underlying lung pathology which is pressing upon the diaphragm and causing pain.CT chest may be needed.Chronic pancreatitis,cardiac pathology and Functional abdominal pain syndrome (FAPS) may also cause this kind of pain.
Splenic enlargement and ovarian cysts in females can also cause such pain.
It would be better to get CT abdomen done which can clear cut confirm a diagnosis from the above possibilities.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.