How can I tell if my breastfed baby was fed formula? He spent the night with relative Sunday night. he was sent with plenty of stored breastmilk. Last night he was super duper fussy and this morning his poop was not the same as usual. It was almost solid and smelled much different. He just started apples and has had pears before and his poop still seemed more like breast fed baby. I don't want to blindly accuse but if he was fed formula I will be soooooo mad. I won't be able to ever trust them if I don't find out for sure though. Help!!