Just do it at home
Depending on your symptoms(assuming they are not severe in any way) best thing to do is avoid all dairy products for 4-5 days, and be sure your symptoms are all gone.
.Then try a small amount of cheese or milk..If the symptoms recur...Do the same thing....If it happens again you probably are lactose
intolerant...Then try many of the tasty lactaid products or use lactase
pills, found in most stores.