gastritis is just an irritation of the lining of the stomach. The trick is figure out what is causing it. Most likely the doctors will just give you an acid reducer. But unless you have acid reflux, this wont dont anything.
My suggestion is to alter your diet. Stay away from foods that are hard to digest or foods that are stomach irritants. These would be red meats, fatty foods, highly processed foods, acidic foods, soy, gluten, and dairy. It will not be easy, but if you remove these types of food from your diet you will notice a difference.