Most often gastroenteritis in children does not need treatment with antibiotics. Giving ORS (oral rehydration solution) to prevent dehydration is important. 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 as the mainstay of treatment. Treatment is not supposed to bring down the frequency of passage of loose stools. Giving vomiking 15-30 mins before the feeds or before giving other medicines, will prevent the food or medicines from being vomited out. 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 unless the child grows lethargic, I would not get concerned. It may still take 3-5 days (from the onset) to stop. The other medicines that you are giving, are proper. (I do not however understand what you mean by oral injection.) Zinc supplementation will help in the intestinal healing as the diarrhoea causes some damage to the inner wall of the intestines. You may also give some amount of yogurt/curd as it contains beneficial bacteria.