what about the temperature? this is very important for babies this age.

if the cough continues for more than 4 days, u better bring see doctor.

if u feel any doubts, can always just bring to see doctor any time u want though.

but if temperature is high, just go.
also, any changes recently?
could be the baby's body reacting to new milk, or something new, and is allergic to it.
coughing is a defence mechanism.