my little guy is a month old and is breastfed. he gets formula once a day. he's been having alot of…

my little guy is a month old and is breastfed. he gets formula once a day. he's been having alot of trouble pooping this last two weeks. it's a little clayish and is still yellow though. I'm just trying karo syrup. it got him to poop one diaper full. but he hasn't pooped for four days. negoew he was pooping once a day. is there anything else I could so? he cries out when he tries to poop