My 6mo old son is whining and crying a lot and feels warm, He's not drinking the full 5oz he always…

My 6mo old son is whining and crying a lot and feels warm, He's not drinking the full 5oz he always drinks and has been crying a little more at night. I called his pediatrician and they said since it's not over 101 to give him tylenol and keep checking up on him and call again if he's not getting any better. He has been drooling and chewing on things, Could it be that he's theeting??