M.B.
Are you sure it's just lactose intolerance and not a true dairy allergy? I spent 10+ years thinking I was just lactose intolerant, but finally found out when I was 40+ that it was a true dairy allergy to casein. Whey protein also causes problems. Also, soy is another very, very common allergen, so you might try rice or potato milk instead. And, soy can cause very similar symptoms as a dairy allergy/lactose intolerance. Also, food allergies rarely occur in isolation and most folks have multiple, with the top allergens being: Eggs, fish, shellfish, wheat, dairy, soy, nuts and peanuts. So, you might try eliminating all of those for a couple weeks and then add back in one by one (leaving at least 3 days between adding anything new - food allergies can be delayed up to 72 hours after exposure).