How can you tell if a baby has diarrhea since baby poop is soft as is?

DS is 4.5 months old. DS doesn't go daily (he'll go within 48-72 hours usually), but when he does go it's large and explosive. It looks kind of pasty and somewhat wet. He's having plenty of wet diapers, eating well, and is his normal behavior. Just wondering if I should contact the pedi and bring in his diaper for examination or not.