You may need a calcium supplement and other foods that contain calcium. Here is a list of foods containing calcium besides dairy foods you may like. Calcium amounts also listed. You can buy milk products treated with lactase to reduce the lactose content. You can also buy lactase tablets or drops to treat regular milk.
Some people also use soy infant formula or soy milk fortified with calcium.
The calcium content of soy milk can vary a lot so check the nutrition label carefully. Calcium supplements are absorbed better in doses of 500 mg or less. You may also need a Vitamin D supplement along with the calcium. Most of the time, symptoms of lactose intolerance are mild. If you have more severe symptoms, you may have a more serious problem.