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The most important thing to do is Endoscopy
will not show the stomach - for that matter anything with gas!
Prokinetics like domperidone
(nausea) / antiflatulent like simethicone
(gas) / adsorbent like activated charcoal - are some of the medicines that help...
Gas can be produced in the intestine from certain foods.
Gas is not produced in the stomach - there is generally the swallowed air. Munching and swallowing with closed mouth helps to reduce.
Sometimes, id could be Psychological - aerophagy and belching
See a gastro-enterologist.. be investigated properly. Everything will be well
Wishing speedy recovery