Many people suffer from lactose intolerance, where they are unable to digest anything that has lactose in any form. This includes milk, cheese, yoghurt, and other milk based sweets.
The best way to treat it is by avoiding food of this type and by having a tablet like Lactate before your meals.

    

Well this disorder is very effective to the mechanism of body. I would suggest some preventive tips:
1) Eat low-lactose cheddar or Swiss cheese.
2) Pretreat milk yourself with over-the-counter lactose formulas, such as Dairy Ease and Lactaid. Adding the liquid form to milk and then letting it refrigerate for 24 hours can hydrolyze up to 99 percent of the lactose.
3) Gastric discomfort may be less if you drink milk with meals instead of alone.