I'm pretty sure I'm lactose intolerance but how can I be tested?

Not so easy. 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.