I'm going to see a gastroentologist for severe heartburn in 2 weeks. What should I be keeping track of? What should I expect?

Symptoms, diet, time. Expect a comprehensive history (cardiac questions too), physical exam, rectal exam probably, check stool for blood, labs. Maybe endoscopy depending on duration, severity of symptoms, age, risk factors for ulcers, chronic esophageal changes. Keep track symptoms, time of day, awakened at night? Triggers, relief, duration, other symptoms (sweats, short of breath, palps, chest discomfort etc), meds.
Monitor food. Keep track of any relation to foods. Type of food as well as time of day that the symptoms are worse. Does the heartburn get better or worse with food?