Hello Akhand and welcome to HCM
Its good that you have started antibiotic but don't know the time period? An oral administration of antibiotic takes about 12-24 hours to get into action. Wait for one day after staring the antibiotic unless the frequency of loose stool
increases and your son is unable to take oral fluid. If frequency does't decreases the try to change the antibiotic or admit your child for I.V. administration of antibiotic. follow some precautions:
Keep your son hydrated, use only boiled water or RO filtered water.
or electrolyte powder to get rid from electrolyte imbalance
Give only fresh diet or juice.
Keep a check on urine output if it decreases or stops than immediately rush to ER.
This will surely helps you.