There are other substances found in milk products - other than lactose - that could be contributing to the problem, so you might want to try a completely dairy-free diet for about two weeks to see if that improves anything. It's difficult, because dairy is in a LOT of things and you have to closely read the ingredients' label to make sure you're not ingesting any of it. Sometimes taking Lactaid pills just ain't enough!
You also might want to consider getting a stool test for giardia, which can cause really foul-smelling flatulence and stools, bad stomach cramps, and diarrhea. It's a pretty common parasite and can be a real pain in the you-know-what but is easy to treat! You'd need to do three separate stool samples in order for the test to be fairly reliable. Ask your doc about it! Good luck, and keep us updated.