Try the best whole-leaf aloe juice u can find. The best I have found is rated 150% 75% juice, 25% water. Aloe council standard is: 100% aloe juice product consists of 50%water/50% juice. A good calcium formula, preferably in "isotonic" capable form should help. Also consider digestive enzymes and probiotics.
One or two ginger capsules are very good for nausea. Might be good for the gastritis too. Ginger is relative cheap and it would not hurt to get a small bottle and give it a try.