Sudden change in poop consistency

A little gross, but wanted to see if any other moms have experience with a change in their little ones poop. My son is almost 8 weeks old and up until last week had been having yellow paste-like poop, then suddenly he started having larger blow outs that range from a little watery to very watery, like this picture, I'm also not sure of the flecks in the poop either. I know about seedy poop, but this looks different. There is some mucous, but not a ton. He is breast fed, with a small amount of formula added to thicken the breast milk, which we've been doing for 4 weeks. He hasn't been showing any other signs of dehydration, he still has plenty of wet diapers, and no fever or increased fussiness. Just not sure of the change in consistency all of a sudden.