Are u breast feeding him? Exclusively breast fed babies can pass stools once in a week even but still the stools will be soft and he will not strain while passing stools.
If he is on infant formula
, be sure he is getting adequate feeds in the recommended dilution.
You may try concentrated sugar solution prepared hygienically at home.
If you feel he strains while he is passing stools or if the stools are big and hard or if you see blood in stools, please take him to your pediatrician
Hope this answer helps you.