Here's a site with a few user suggested remedies for gastritis: EarthClinic. They list some of the things you've tried but also lists others. Here is another EarthClinic page that discusses gastritis.
One of the comments in the multiple remedies sub-section says this:
That reminded me about l-glutamine being useful for healing the stomach lining. Here is a search with lots of results about the topic.
Cayenne might help as well:
One of the comments in the multiple remedies sub-section says this:
I have had Gastritis and all they want to do is give me nexium and the such which I found gave me other issues over the last 6-7 years. I think it is from taking meds in the morning and coffee so close. My take. And in the last few years I would always take 1-2 "GAS-X" capsules which would help. Ususally I get so bloated that lying on my side or later in my sleep , wake up with stomach spasms and heart palpitations. No BLOATING.. Can drink with meals.
I found this website a few months back and have been doing a number of things including ACV & baking soda with a 500mg of L-Glutamine (vitamin supplement) with each of the 3 8oz of the ACV tonic. DOES NOT bother the stomach.. In fact I have felt great! No palpitation issues over the last 4-5 weeks. I am very happy.. People look at me sideways when I tell them I am taking this stuff. The answer with so many folks is prescriptions ($$$). I also stopped dairy, cut down on coffee and taking 600-800 mg of "chelated magnesium", added B12s, sublingual 1200-2400 per day.
That reminded me about l-glutamine being useful for healing the stomach lining. Here is a search with lots of results about the topic.
Cayenne might help as well:
from: http://cayennepepper.info/health-benefits-of-cayenne-pepper.html
"Notwithstanding its hot taste, paradoxically it is actually superb for rebuilding the tissue in the stomach, facilitating healing with stomach and intestinal ulcers. Cayenne pepper for ulcers is not something most would have considered but I can testify to that remarkable capability of this remarkable medicinal spice."