Thanks for your query.
Your baby is having diarrhea
which is mostly viral in nature and takes few days to settle.
Continue with medication as advised.
Most important is to maintain hydration.
I suggest you to give more breast feeding than formula feed,if you have to out ,expressed breast milk can be given.
Give oral rehydation solution sip by sip after each loose stool
Watch for features of dehydration
like decreased urine output/lethargy/refusal of feeds/sunken eyes and in case you find any get him re evaluated by pediatrician
Regarding lactogen ,you can give it,there is not much difference between the two.
Moreover after 6 months of age start complementary feeding as well .
Wishing your baby good health.