Gastritis, which is inflammation of the abdominal lining, could cause abdominal pain, gas and a bloated-ness, feelings of nausea, vomiting and perhaps a burning.
You will want to avoid highly acidic foods such as citrus juices or tomato based food products (eg. spaghetti, pizza).
You should also avoid alcohol & smoking, caffeine, and any spicy/highly seasoned foods.
Try eating smaller more frequent meals (or snacks) rather than the typical 3 large meals a day.
Some foods are not good for an upset stomach. Foods that are high in fat, contain fiber, are spicy and are greasy can cause further gastric complications. Avoid dairy products if you are actively vomiting or have diarrhea. Do not eat or drink foods or beverages that contain alcohol or caffeine, because these substances can promote dehydration. Avoid black pepper, chili powder, chocolate, carbonated beverages, fried foods, acidic fruit juices such as orange juice, broccoli, corn, onions, cabbage and cheese. Avoid eating large amounts of food.