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 as it may make your gastritis symptoms worse...consider calming activities, such as meditation, yoga etc...I would advice you to take pantoprazole 40 mg once a day before meals along with Domperidone 30 mg and a probiotic...further treatment depends upon stool examination reports Consult nearest physician they will do the needful.
Loose motions is causing pain in the stomach. You need to take medicines for loose motions and you will be fine. Since you are in London, taking pills over the counter might be difficult so you can try this home remedy- mix half a tsp of dry roasted jeera with a pinch of salt and mix it in half a cup of yoghurt. Take one tsp of this mixture every two hours. Besides drink ORS solution time and again as you should be well hydrated.