Stomach gasses might originate from both exogenous and/or endogenous sources. Swallowing air might cause belching. Inadequate digestion might cause flatulence due to gasses released during fermentation.
You might try to avoid food rich in certain types of polysaccharides (especially inulin) which include beans, lentils, dairy products, potatoes, radishes. Some food like cabbage, cauliflower and broccoli do not increase the quantity of the flatus, but its pungency. If this does not help, you might consult your family doctor if digestive enzyme supplements are needed.