Tsarevna...let me know what you find out. I have been experiencing something very similar for over a year. I had all the upper and lower GI endoscopy done, as well as an MRI of the upper abdomen. My gallbladder has been gone since 1999. They are finding nothing and treated me for H-pylori and acid reflux. (The antibiodics made my stomach hurt as much if not more.)
I recently went back to a natural path doc that I had seen a few years ago. Based on the PH tests done with saliva, I do not have acid reflux. So what we are doing now is a regimen of supplements (expensive) for balancing stomach and GI PH and flora. I continue to go gluten free in my diet, drink aloe juice everyday, eat yogurt and take ACV (apple cider vinegar). I've only been doing the supplement regimen less than a week and unfortunately still have some problems, mostly with the awful fullness feeling after eating and a pressure type feeling in my upper stomach which comes and goes. I am hoping that symptoms will improve...my logic being that it didn't take a few days to get out of whack, so it should take more than a few days to get things back to normal. My gluten free eating has been since last summer and my lower GI has improved immensely...IBS is NO fun.
I have also read that ginger and garlic are good for stomach issues as well as a certain type of licorice.
Have a great day!