Heartburn even after a small meal but never when my stomach is empty.y? is it because of low stomach acid or excessive?

Heartburn: Is usually due acid backing up into the esophagus. It can occur in the presence of normal acid production or with excess acid

Heartburn.: It’s related to the way GERD/reflux works. Upon food entering the stomach, the production of gastric fluids increases. These fluids then enter the esophagus, causing the symptoms you feel as heartburn because of the acid content of the fluids. They enter the esophagus because of incompetence of the sphincter that normally separates the stomach from the esophagus (hiatal hernia).