Thanks for your query.
your son is having features of acute gastroenteritis
which in most case is viral in origin and takes its own course.
Antibiotic is helpful only if it is bacterial in nature.
Most important is to maintain hydration.
Give oral rehydration solution sip by sip after each loose stool
,give coconut water,lemonade,curd,mashed banana.boiled potato.
Give lactobaccilus for 2 to 3 days and zinc for 14 days.
Watch for features of dehydration
like decreased urine output,lethargy.
In case symptoms persist get him evaluated by pediatrician
Wishing your baby good health