Does he seem happy otherwise?

I have no experience dealing with a child doing this personally. I vividly remember my younger sister being about the same age and doing this as well. I think it was her "testing limits with boundaries" age looking back. Also what are you feeding him? A lot of parents have issues with most commercial breads (that is apparently one of the top culprits in preservative issues) and see immediate results when switched to a preservative free bread (Brumby's is all preservative free). It's always hard when you hit one of those periods in raising children! I hope it works out quickly!