My 16-week-old baby has started having very smelly and dark green poop. Initially, it was of normal consistency, but today, after not pooping yesterday, it became harder and had a clay-like texture. Despite this change in his bowel movements, he is playful, active, and shows no signs of distress such as fever or vomiting. Should I be worried about this or is it normal for babies at this age? Should I take him to the doctor?