DS is 15 weeks old and seems to constantly have really loose stools. he only goes once a day, and when it goes it is yellow runny and slimey, not completely watery but still runnier than I'd expect. its like he stores it up all day and then does a huge one at once. he always seems irratable for a couple of hours before he goes and once he's been he's like a different baby. He is FF. is this normal? could it be teething? No fever, no other signs of illness.