My lil one has had diarrhoea on and off over the last week he has been the docs who has said to just keep an eye on it. I regularly check his mouth to see if he's teething and I think I felt some sharp ridges at the back of his mouth. To questions really can teething cause diarrhoea (why?) and I thought it was the front teeth that came through first. My DS is 5 months on boxing day.