try eating several small meals instead of three large ones whenever you can...Avoid foods that irritate your stomach, especially those that are spicy, acidic, fried or fatty... avoid coffee,tea etc... Avoid stress,consider calming activities, such as meditation, yoga etc...sleep with head raised position and have dinner at least 2 hours before sleep..

It may be due to many reasons but the most common cause of stomach infection  is usually amoebiasis. You take a course of anti amoebic treatment with Metrogyl 400mg three times a day for five days. Tab Pentocid 40mg once a day for five days. If the things don't improve, it would be better to consult your family physician for better understanding of the disease and treatment. Ensure that you take your meals regularly at proper timings. Avoid use of tea, coffee and aerated drinks. Proper rest and exercise are equally important.