4month old crying when pooping

Zainab • 2 early MC, 1 baby and another BFP hope this is my second rainbow baby
My 4 month old is exclusively breastfed and ussually poops without any problems. Since yeaterday she cries when trying to poop and pushes/ grunts loudly which isn't ussual for her. Her poop is also smelly not like the usual smell. Other than that she is completely fine. Good amount of wet diapers, active and happy. Has this happened to anyone?