3 month old breastfed baby ate a lot, then was being very fussy then had green very smelly poop. what could cause this?

Common: The list of causes for fussiness is endless, but pretty common for young infants.Stool color is defined by pigments added by the liver, which start out a dark green and change through lighter green/yellows and browns depending on how long it takes to move through digestion and how the germs act on it. The scenario is not uncommon or worrisome.