Thanks for posting your query at HealthCareMagic. You are talking about diarrhoea in a 4 month old child. You have not indicated whether your baby is exclusively breast fed or is on milk substitutes. Usually it is caused by a virus called rotavirus. In case of feeding with milk substitutes, irrespective of how well you sterilise the containers, there is always a scope of contamination. It is therefore quite common for bottlefed or spoon fed babies to have recurrent episodes of diarrhoea. Breast feed is therefore always the best. In case of milk substitues, ORS needs to be given in case of diarrhoea. In case your baby is breast fed, continue breast feeding as it it better than ORS. This is important so that the child does not lose salt and water from his body. The frequency of passing urine will indicate whether the feeds are adequate. Continue the medication prescribed by your doctor for the prescribed duration. Hope I have been able to address your cause of concern. Feel free to revert back in case of any other further queries.