Lactose intolerance might not be as bad as you think.
If you're currently lactose intolerant, you shouldn't quit drinking milk all together. It is a good source of calcium. However, it's not a good idea to drink a lot of milk on an empty stomach. On an empty stomach, dairy moves faster through your intestines and is more likely to cause you intolerance problems. Also, if you seldom consume dairy, you're more likely you to encounter problems.
Your so-called intolerant intestines actually have the bacteria they need to digest dairy, but you have to train them to do it, so to speak. So if you have problems with dairy, keep drinking milk, but in small doses and with meals. Drink say, half a cup of milk, three times a day with food. And regularly. The symptoms of lactose intolerance will not only be minimal, but within just a few weeks, you will probably stop suffering from lactose intolerance altogether.
As a rule, always consume dairy in moderation. And try yogurt. They contain bacteria that help you digest lactose easier. Also, if you suffer from diarrhea due to something like food poisoning, note that you will likely have to retrain your intestines.