Sudden change in baby’s poop consistency and colour?

Am

My son is just about 5 months, he is exclusively breastmilk fed. He has had no solids.

Up until now, his poop has always been bright yellow and runny. Not watery but not formed at all. All of a sudden today, it was like a yellow/brown and like peanut butter consistency. He has been cranky today so idk if it’s related. Is it weird that it all of a sudden got thicker without any change to his diet?