I have gastritis and IBS as do a few of us here. Managing the diet etc. is a juggling act. I follow the low FODMAP diet for the IBS and that helps a lot. I always view each new ingredient as a potential risk fir gastritis. If it's ok with that I explore how much the IBS will handle.I have sensitive teeth and the St. John's wort I tame for my anxiety has helped that.

I have both as well, and multiple food sensitivities.
I've found eating gentle foods with soluble fiber to be helpful for both. I can't handle metamucil and such, so I try to get it in food.
Also, taking slippery elm keeps things moving. I tend towards IBS-C after having IBS-D from age 5-40 it suddenly switched over about then, no clue why except that I did get my celiac diagnosis then and cut back on wheat.
At this point there is a list on the fridge and in my phone of the foods I can eat without either acting up. It's limited but it is what it is....

For my IBS I follow a gluten-free diet, it helped me tremendously. I follow loosely the fodmap diet as well (mostly avoiding beans and cabbage).
For gastritis I follow a low acid (nothing below ph level 5), bland, low fat, low fiber, non irritating diet.
For my teeth I use a sensitive toothpaste and a sensitive mouthwash (elmex, green).

Whenever I have had really bad days in the past I always say to myself I would gladly lose all the foods in the world to have no pain. Of course IBS doesn't follow rules. Love the FODMAP diet as I now eat foods I thought I had to avoid - I simply limit them as per dieticians advice.

Probiotic brand "Align" was proven clinically to aid people with IBS.

Also, since you have MS and you're on PPIs, you should really consider sublingual methylcobalamine, the most effective form of B12. It could make random nerve-ending sensitivity go away. Get the 5000mcg version from Jarrow (on Amazon).

I have heard the same thing about Align. I have tried it and did not notice any difference though but I don't have diarrhea.

Soretum, I was wondering. The problem with B12 is that we don't process it because of the low acid in the stomach. I saw the sublingual B12 at the store, but I was wondering if it solves the problem. Does the sublingual B12 go directly through your system by the mouth, or does it have to go through your stomach too and so we are back with the same problem of low absorption because of low acid? I could not find any scientific study about this or anything convincing really.

My question was for sihonnage, sorry...

Ines..

The sublingual B12 liquid that you put under your tongue is the way to do it. It gets absorbed way more effectively.

I'm glad that was cleared up. I know nothing about that.

You put the hard pill under the tongue and it gets absorbed that way. It also goes in the stomach, obviously... not sure what happens there. It probably gets partially absorbed due to being a high dose.

Fodmap diet has helped me tremendously.

Do you have flare ups for no known reason in cooler weather, with the IBS or the gastritis? I know some of is do.