Gastritis Support Group
Gastritis is a medical term for inflammation of the lining of the stomach. It means that white blood cells move into the wall of the stomach as a response to some type of injury. Gastritis has many underlying causes, from infection with the bacterium H. pylori, bile reflux, or excessive consumption of alcohol or certain foods or drugs like aspirin.
2) When acid reducers don't help at all, but Betaine HCL helps a lot, you have low stomach acid.
If Betaine HCL hurts a lot, then you have high stomach acid, and are damaging your lining further by this experiment.
You're probably better off getting a gastroscopy to help your doctor answer this.
3) Not sure
Also see:
http://scdlifestyle.com/2012/03/how-to-supplement-with-betaine-hcl-for-low-stomach-acid/