No D Milk for Little Man

So, our litttlest monkey bear can't seem to keep his cow's milk down. I am trying to transition him from my mama's milk to cow's milk, Vitamin D. Why is he running round in his diaper? He vomits all every time he finished even the smallest bit of milk. As far as taste, he doesn't seem to like the cow's milk much either. He runs from me like this when I try and give it to him:

Or, he makes faces like this as he drinks:

But since I've got him in his diaper I think we should get a gander of those baby chubbies:

Milk mustache:

This baby has no but to hold up those diapers. How did that happen, Theo and I have huge arses?