try to give him some pepto...My dogs went through the same thing about 2 weeks ago...there is a virus going around here for dogs, and its not the  dog flu virus is just 
diahrea, some blood and  mucus, it starts out brownish then its yellowgreen color...I took everyone of mine to the vet and no parasites he said its something going  around...oh by the way all of my acted normal, ate, was drinking water and playing as normal...good luck hope this helps, it last about 4 to5 days...