If he has completed 5 months of age,start 1 solid meal including curd and Banana in the diet in addition to whatever you prepare at home,and 5 milk feeds including one top formula feed using a spoon and katori. Give ors after every loose motion if watery and add Enterogermina vial half vial twice a day for 5 days. If not improving in 3 days OR accompanied by other symptoms like vomiting or fever or dullness and refusal to feed,consult your paediatrician asap.