Sixty percent of adults can't digest milk
The long lists of food allergies some people claim to have can make it seem as if they're just finicky eaters trying to rationalize likes and dislikes. Not so. Eggs, peanuts, tree nuts, fish, shellfish soy and gluten all can wreak havoc on the immune system of allergic individuals, even causing a deadly reaction called anaphylaxis. But those allergic reactions are relatively rare, affecting an estimated 4% of adults. Ref. Source 3
Well, I am not sure if I fit in that category. My case maybe is unique, not sure. I can eat all dairy products with no problem whatsoever, including milk in mash potatoes, etc. The issue becomes a problem when I try to drink milk either alone, with chocolate or with my cereal. I get very sick (stomach ache) and then straight to the bathroom.
You just described my wife 15 year ago. Now she cannot eat any eat or drink any milk product. I caution you to watch out on your iron levels as well. vitamin D and iron go hand in hand. Oh and calcium if taking too close to iron prevents your body from absorbing it.
In my opinion your lactose intolerant. It is becoming more common then ever....I think it is due to the over processing and filtering of milk. it removes too much of the lactates enzyme that helps a person break down milk. This is why doctors recommend goats milk it has higher levels of this enzyme making it easier to drink and digest.
As for me I just am not crazy on its taste so I leave it alone.
I think a lot of people are getting to where they can not handle milk in its more raw form. My wife can eat eggs, cheese, instant mashed taters, and yogurt with no problem. IF she eats cereal or drinks milk then she has problems later on. I believe that Krakyn is correct this is due to over processing of the milk. I think we would be better off if we did not process the milk products as much.
How long has it been like that? My wife in the mid 90's developed reactions to milk then over the next ten years it moved to include more milk items but with a far smaller reaction. Cheese Swiss is fine cheddar OK feta she vomits. Yogurt she can eat with no reaction at all. A friend of ours can not touch any milk at all without a loose stool. So I would not rule it out but instead move to alternative and see if you feel better.