Breast milk is the best for your baby. Till 6 months exclusive breast feeding is the best.
As you feed him more, your milk production will increase as sucking by baby is the best stimulus for increasing the milk production. So do feed him frequently.
If you are giving formula with bottle- stop it immediately. Bottle if not sterilized well is the major reason for such diarrheal events.
Stop dexolac temporarily. You may try soyamilk (ISOMIL) instead for few weeks.
You may give probiotic
sachet like Econorm/ Bifilac
with advice of your Pediatrician
When kids get diarrhea, temporary lactose intolerance
happens, so formula milk will not be tolerated. In extreme cases nil lactose formula like Lactonil can be tried.
Wish a speedy recovery for your kid.