If you are still bothered by symptoms, then you may want to try less milk and either increase your consumption of other foods high in calcium or take calcium supplements. But LI will be the least of your concerns. No problems and no limits, although after the first few you're probably not going to get much additional help by taking more. For more information on everything lactase, see the Lactase page in the LI Basics section of my web site. The gas almost always comes out the other end.
Lactose is milk sugar.
It has absolutely nothing to do with calcium. The only way to tell whether a product is lactose free is to study the ingredients list and make sure that there are no milk products on it. As far as I know, no infants are ever allergic to mother's milk itself. The allergy is to something in the milk. It is possible, if the mother is drinking cow's milk, for some of the proteins to filter through into the milk.