anyone else's DC vomit when they have whole milk?

hippotree

We started Henry on whole milk when he  was 11.5 months and he did fine.  Last week he started vomiting up his entire bottle every morning.  He's also been having some severe constipation issues since we switched him to whole milk, so we switched him to soy this week (he hasn't had whole milk since Monday).  Tonight I gave him a little whole milk mixed in with his soy milk and sure enough, he puked up his whole bottle.

Obviously he won't be getting whole milk again for a long time, but I was wondering if anyone had any ideas as to what is causing this and why it started so suddenly?