Your symptom description suggests you might have a sensitive stomach and bowel, which are the most common causes for GI symptoms at your age.
The problem of passing gas could be related to the diet that you consume. Please avoid too much of garlic and onion.
You may want to check on FODMAP diet on the internet, as diet high in FODMAP can produce abdominal bloating and flatulence.
Gastritis means inflammation in your stomach, which could be non specific or due to certain causes like Helicobacter pylori infection or painkiller. Irritable bowel syndrome points to bowel sensitivity.
Dr Loh PY
Consultant Gastroenterologist