Hi dbwilco. I was on oral ABX for 10 months, and had to stop them in the end due to severe gastritis. I had all of the symptoms you mentioned after having been on several meds -- doxy, omnicef, azythromycin, mepron, ceftin and bactrim -- and often on 3 at a time.
I stopped the antibiotics for 6 weeks and worked on healing my gut/boosting my immune system. My stomach healed (though my LLMD thinks I could have had a small ulcer). I didn't have an endoscopy because my symptoms rapidly improved after stopping the medications. I did, however, have a stool test done and did not have candida or parasitical issues, so that useful to rule out.
I am now on intramuscular Bicillin shots, and I think they are really making a difference. They have caused the worst herxes I've ever had, and arriving at the right dose has been a challenge. But, I think I'm getting there.
Just know that Bicillin is a potentially useful ABX should you wish to take a break from orals and have an LLMD who is willing to consider them. It may or may not be covered by your insurance, though in my case it has been.
In the meantime, one product that I really found helpful (because the traditional PPIs didn't seem to help) was Gastrex by Standard Process. It's plant-based (okra, I believe) and really helped heal my stomach as did Slippery Elm power (mixed in water) and Enteromend (which contains aloe vera, L-Glutamine among other things).
Hope you feel better soon,