Pigs rarely vomit, but if they do, I am usually concerned about a gastric ulcer. Ulcer pigs tend to be off-feed too. If an ulcer gets bad enough, the pig starts bleeding into the stomach and you see dark, tarry digested blood in the poop and the pig gets really pale from the blood loss. I start by feeding ulcer pigs high fiber, easily palatable feedstuffs, like rolled oats or alfalfa. Some people try some Tagamet too with varialbe results. AGain, not for sure if this is what is going on with your pig, but ulcers are always the first thing on my mind with puking pigs.