As a fellow "lactose intolerant", let me tell you that I feel your pain. I have a great story of how I became lactose intolerant a few years ago. It involves a van full of triathletes from the Olympic Training Center, a case of bottled milkshakes and a dare, but I won't go into details.
Lactose intolerance is due to an inability to digest lactose, the sugar in milk. Symptoms include abdominal discomfort, bloating, nausea, diarrhea, cramps and gas. Tests that your physician can order, besides completing a good history and physical, include a lactose tolerance test, breath pH and stool acidity test. Most commonly, resolution of symptoms upon avoidance of foods containing lactose are evidence enough to nail the diagnosis.
A healthy diet is still possible despite your inability to digest lactose. Unfortunately for us, foods that contain lactose are excellent sources of calcium, the recommended daily intake of which is set between 1,000 and 1,500 mg/day, depending on your age.
There are numerous "tricks" I've employed that you might find helpful. Probably most important is the fact that people who are lactose intolerant can still eat foods like yogurt with active cultures and aged cheeses (think cheddar or gruyere). Products like soymilk and Lactaid are perfectly tolerated and fortified. Other foods including salmon, sardines and broccoli are good sources as well, and often overlooked. Finally, raw milk has been discussed as a possible source of digestible lactose and/or probiotic cultures that may be helpful in treating lactose intolerance. However, the evidence on this point is not convincing and the FDA does not currently recommend consuming raw milk due to the potential harmful effects of bacterial contamination.
One caveat to obtaining adequate calcium via non-milk sources is that Vitamin D is required for optimal absorption. Therefore, be sure to either include sources like eggs or liver in your diet or get plenty of sunshine!