I have had people tell me that that cannot have any lactose, no matter how small an amount. I think that the condition is rare among people who have lost their lactase-producing ability naturally. If you've ever suffered any problems with your intestines that may have left them damaged, then they may heal in time. Or they may be permanently damaged. Your doctors should be able to tell whether this is the case from your medical history, so if they have not raised this as a possibility, then your problem may be from another cause.
Some people seem to feel the effects right away.
At other times, and in other people, it can be delayed several hours. However, if you regularly have cramping and diarrhea an hour after every meal with lactose and not after meals that have none, then I'd have to say lactose intolerance is a good bet. In any case, I'm glad you're seeing your doctor. There is a very accurate test for lactose intolerance that your doctor can arrange. Of course, most doctors will try to rule out the more serious diseases with similar symptoms first, so don't be surprised if you're asked to take other tests in the beginning.