I have two hiatus hernia, GERD, and have also had gastritis - all started in my early 20’s.
The consultant put an endoscopy camera down, which was left in for 48 hours. The wire came out of my nose, and at the end was a type of remote control with buttons to press when I ate, drank, lay down, or was sick (from what I recall, may have been more options).
The endoscopy wire had sensors the whole way down to measure where the refluxed food and acid reached, and also how my oesophagus was functioning.
It found that the peristalsis function - think of a snake, where the muscles work in a certain order, smooth and rhythmic and without spasm or delay - was disrupted due to scarring/hernia. This cause food to get stuck, refluxed back up, delayed gastric emptying as food sort of bounces around, and a leaky valve at the top of my stomach.
I had already been diagnosed with hypermobility as a child, and was later diagnosed with Hypermobile Ehlers Danlos, which definitely contributes.
I was advised not to have surgery to repair the hernias so young as it would need repeating due to the weakened areas and the possibility of new hernias popping through.
It was a reasonably long journey to recovery, including taking esomeprazole (different to standard omeprazole apparently), complete diet overhaul, sleeping propped up, keeping weight down… but my oesophagus healed and symptoms have been controlled for 20 years (flared during pregnancy).
Definitely worth asking if they can assess your oesophageal function.
I hope you feel better soon.