My 14 yr old son gets daily heartburn no matter what he eats. Normal upper and lower GI scope. Slight pain left side of stomach when applying pressur?

Possible stress. Since you mentioned he had a normal upper and lower GI scope, he must be seeing a gastroenterologist. Is he on any medication? Did he get tested for bacteria during the endoscopy? Stress is one of the most common causes of this symptom, which is from excess acid production. I would recommend that you discuss this again with his doctor.