itchy mouth and diarrhea
lactose just gives an upset stomach

my friend who is lactose intolerant would vomit anytime she had dairy. it was pretty easy to figure out her condition.

Lactose intolerance and milk allergy are two different things. Milk allergy is just like any other allergy – if milk touches you and you are allergic to it you break out in hives. if your allergy is bad enough your throat might close up and cut off your airway.

Lactose intolerance is "the inability to metabolize lactose, a sugar found in milk and other dairy products, because the required enzyme lactase is absent in the intestinal system or its availability is lowered."

If you suspect you might be lactose intolerant you can go to a doctor for testing to find out.