Since new babies stools often look like diarrhea for awhile it can be hard to tell whether the baby is having diarrhea or not.
But usually the babies poop will have mucus or a more foul smelling odor to it than just normal poop smell.
Also diarrhea can cause dehydration too so look for signs that your baby may be dehydrated such as, few wet diapers, dry eyes when crying, Sunken Fontanel, dry mouth, sunken eyes and lethargy.