I've only given L Tylenol 2X in his life - at his 4 and 6 months shots (he is 8.5m). Today he seemed to be whining/chewing/biting more than ever. And i can see his top 2 teeth coming in. So i gave Tylenol before bed. I just don't want this to become a habit. How can you tell when it is appropriate to give or not?