Remember that doctors define a normal amount of bowel movements as anywhere from three times a day to three times a week. Or you may be having a psychological reaction to knowing you're about to eat food that contains something you shouldn't have. It may even be something as simple as having a stomach flu and not realizing it. Not very helpful, I admit. All I can say is that you should try several different brands of lactase.
Some people simply react better to some brands than to others.
You might also look at my Lactase page in my LI Basics section. I gave lots of helpful hints as well as answers to what and when and how and how much lactase. You may find something useful there. I know I don't get enough calcium, so I take calcium supplements. The answer is, probably.