hello, my 4.5 month old baby has had diahrrea for 3 days now, mostly greenish-yellow and mucus-y, because has a cold and cough . but i just changed another poopy diaper and this time, along with the color and mucus, the stool had little black streaks in it. he is strictly formula fed, no solids yet. what could this be and should i take him to our pediatrician?