diarrhoea

How will I know if my lo had diarrhoea? He bowel movements have changed in the last few days, he used to do 4 poos a day now he's only doing one and it seems darker and thicker than normal! they still have seeds in but not what they used to be. He's not in pain when he poos he seems all fine within himself, no temp or anything. He had started drooling a lot more and constantly have to wipe his face he's drooling that much! Any one know if this his poo is normal? Hes 2 months old! Thanks ftm and his change in habit is freaking me out!