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stomach pain in this age is most common due to either gastroenteritis
or jaundice. but with gastroenteritis he may have diarrhea
or vomiting and along with jaundice there may yellowish discoloration of the skin. so you can help him by giving soft diet
and giving some antispasmodic syrup and metronidazole
syrup at dose of 10-20mg/kg/dose for 3 times a days.