This could be due to food poisoning,
gastroenteritis with gastric
reflux, infection like amoebiasis or giardiasis. Take an OTC lactobacillus preparation and yoghurt with your meals. Drink plenty of fluids (clear soups, water, ORS in water, lemonade). Eat light, do not stay hungry but eat simple things like toast, porridge, cereals, crackers, banana, rice, peeled apple, etc. Take ORS. Take over the counter antacid and antiemetic (this SOS for vomiting).