Man, I had all kinds of stomach problems for years. It was a total bitch, and I tried every supplement there was to fix it.
The thing that finally cured it was eating a savagely strict elimination diet and working out what was fucking me. Turns out, there were a LOT of things fucking me.
And I don't mean you just cut out a few food groups and see what happens. I mean I literally ate nothing but steak and white rice for 2 months until my symptoms had been gone for a couple of weeks, then I introduced new foods one at a time over the course of several more weeks. It was absolutely brutal but I have not had stomach problems since.
Some foods I eat now sort of gave me a reaction, but I can control it with saccharomyces boulardii and drinking kefir every day (both really good probiotics). If I eat one of my red flag foods though no amount of probiotics can save me.
Turns out I'm sensitive to:
-onions
-garlic
-tomatoes
-anything really fibrous like lentils, chickpeas, etc
-broccoli
-nuts
-processed meats (I have no idea why, maybe some kind of oil in them)
-foods cooked in shitty oil in general (although I never really eat those)
-high amounts of fructose
-avocados
-most high FODMAP foods
-whey protein
-spicy food
quite an extensive list! Before I did my elimination diet I was eating a few of those foods every day because they're good for you, right? Turns out not so good for me. I'm telling you my list just to show you the range of things that can cause problems.
Now I pretty much live on meat, white rice, bell peppers, spinach, white potatoes, eggs, berries and oily fish. My stomach feels amazing and has gone from being bloated as shit every day to flat as a pancake. I never get gas and bowel movements are not the low point of my day anymore (I am trying not to be gross here).
So if you haven't tried a really strict, methodical elimination diet then I would definitely give it a go. In my experience, nothing will improve your gut health until you eliminate the trigger foods.