Thank you for your query on Healthcare Magic.
Your child is having an infectious diarrhea
with a gram negative bacteria.
The infection usually responds to a sensitive antibiotic and loose motions will decrease.
In spite of a week of antibiotic course, the loose stools are still persisting means your son require reevaluation and reassessment to consider antibiotic by intravenous route.
At the same time stool to be tested for routine and for reducing substances to look for any development of lactose intolerance
and zinc can be added to his treatment with the doctor prescription.
Consult your Pediatrician
again for reassessment and further management.
Hope I have answered your query.