When my daughter was younger we found that milk made her very mean and she acted up soon after she had diary products. All of her doctors told us we were crazy, that there were no allergens in milk. We had only anecdotal evidence that milk was causing the problem, but that eveidence enough for us. We withheld milk and things were hunky-dory. We gave her milk and Dr. Jekyll turned into Little Ms. Hyde.
She outgrew this by about the age of 7 or 8.
I have had a milk allergy all my life, but only realized it a few years ago. I was raised in the fifties and hated milk, but was forced to drink it, particularly at family gathering on holidays. I always got car sick on the way home. Today dairy products make me vomit if I am not careful. For example eating a big meal late a night at a conference I go to every year, had me up all night vomiting. I found that I needed to cut out the dairy to avoid this problem. I also found that eating lot of raw carrots will counteract the problems to some degree. And yes, I did tend toward the hyperactive, but my natural avoidance of milk probably kept it at bay.