Hi welcome to HCM... As you are taking chemotherapy , by its side effect you can have gastritis or small gastric ulcer leading pain.... For that acidity should be reduced by antacid like omeprazole on empty stomach before meal for two week.... Avoid gastric irritants like .... -excess tea and coffe -smoking -non veg food -excess spicy foods etc.... Here you can have functional constipation associated as gas formation is there ... For that diegene syrup can be taken... Include more fiber in diet like wheat bran , whole grain , apple etc... Avoid gas forming foods like ... -onion -cabbage -cauliflower -turnip etc.... Take care Advise : gastroenterologist consultation..