Visit your doctor or a gastroenterologist who can test if you are lactose intolerant by conducting a Hydrogen Ion Breath test or a Stool Acidity test. You can also "diagnose" yourself with the simple test below, which has been designed to help you determine if you are lactose intolerant:

Eat normally but avoid all dairy products for 3 days.         On the 3rd day, with an empty stomach, drink a glass of milk (12 ounces) for breakfast (it can be any kind of milk: whole, fat-free, chocolate etc.).         Over the next 6 hours, keep track of any discomforts you may have and how severe they are. If you are experience any unusual discomforts such as flatulence (gas), diarrhea, cramps etc, it is likely that you are lactose intolerant. You may wish to consult a physician for verification.

Note: This test is not for individuals with a known or suspected allergy to milk protein, or who has Irritable Bowel Syndrome or Crohn's Disease. Please consult a doctor for verification. This test may only give insight into possible lactose intolerance.