Could it be a reflection of his diet? If he eats mostly whole grains and fruits/ veggies, this could happen...you know, not much dairy/meat/protein? Fwiw, my ds had poops like this until beyong three years old. Does yours poop frequently, or a "normal" number of times? I think you are wise to look into allergies and sensitivities. My ds is quite a challenge behaviorally and we never really pursued any of that.