My 15 wk old baby is constipated

Hello Dr Mom,

my 15 week old baby is constipated. I am visiting my family for Christmas and my mom persuaded me that I had to give him baby rice cereal in his bottle to fill him up. I caved in and did this for a couple of days, albeit a very small amount. Since then in the last 6 days he's only had 1 bowel movement and it was very different from his regular bowel movements - thicker and smellier. I think he's really uncomfortable now as he's always kicking his legs and passing gas when I breastfeed him. He's also started to writhe and squirm when feeding and won't take a full feeding. Is there anything I can do to help him? Thank you Samantha Tweet