Most likely your son is suffering from food poisoning or acute gastroenteritis. Unless associated with bloody stools, the condition is self limiting. It is unlikely to be flu or food allergy. Give ORS (Oral Rehydration Solution) and plenty of other fluids. It comes in ready made form or may be prepared by mixing a full sachet in the designated amount of water. Replenishment of the lost water and salts is the mainstay of treatment. Unless that is done properly, the dehydration can make the child feel tired. Treatment is not supposed to bring down the frequency of passage of loose stools. The adequacy of the hydration would be evident from the frequency of passage of urine. If that seems to be fine, you need not worry. But if the child grows lethargic, I would get concerned and would suggest taking the child to a hospital without delay. It may still take 3-7 days (from the onset) to stop. You may give zinc supplementation with Zinconia Syr 5 ml twice daily for 5 days. It will help in the intestinal healing as the diarrhoea causes some damage to the inner wall of the intestines. It is preferrable to avoid milk and wheat based items for a week or so. But you may also give plenty of curd or yogurt. It contains plenty of beneficial bacteria and is supposed to be helpful in such a situation.