My whole family has an intolerance to milk. My husband had it as a baby, got better, and developed a problem again in his early 30s. My 5 yr old was put on soy milk @ 15 months due to incurable diaper rash. My 2 yr old was put on soy formula @ 2 wks b/c he would start pooping as soon as he drank his bottle. Finally, I started having a problem when I was about 18 and diagnosed w/ Crohn's Disease. None of us threw up, but I know that my husband and I have horrible stomach cramps. These symptoms can occur immediately or the next day, depending on what we ate.
The good news is, everyone is fine and healthy on Soy milk or Lactaid, the bad news is, Soy milk and Lactaid are more expensive :) We all eat cheese and yogurt, but have a problem w/ ice cream. If my husband really needs his ice cream fix, he takes a chewable lactaid tablet.
My older son has had regular (he calls it white) milk recently w/ no issues. When the 2 yr old gets a little older and more verbal, we'll introduce it to him.
BTW, the 5 yr old is the only one who has had any allergy testing. The milk didn't show up on the skin test, but it did show up in the blood test. When he had the test repeated at 3, the doctor said he could move to regular milk since the levels had gone down. He didn't change b/c he didn't like the taste of it.
Good luck,
T.