it could be gastritis
, but it could be many other things... gastritis can only be diagnosed by an upper endoscopy
with biopsies of the stomach.
You could also have SIBO, IBS, sprue, H Pylori infection
, etc. But i would suggest you starting with some over the counter probiotics, and also simethicone
(gas X), and see what happens, if no improvement then go to see a gastroenterologist.