Lactose intolerance is caused by your digestive system not being able to digest the natural sugar known as Lactose.
When your bodies digestive system cannot digest that Lactose then it leads to lactose intolerance and causes stomach pain, abdominal pain and sometimes vomiting and farting as well.
Lactose intolerance occurs when the bodies small intestine doesn't produce enough of an enzyme (lactase) to digest the milk sugar (lactose).
Normally, lactase turns the milk sugar into two simple sugars which are glucose and galactose at which they are absorbed into the bloodstream through the intestinal lining.
If your stomach hurts after drinking milk then you're likely lactose intolerant.
Most milk contains lactose which some people are intolerant too or have sort of like an allergy to the milk that contains lactose.
So if your stomach hurts after drinking milk then try some lactose free milk and see if that does not hurt your stomach and if it does not then you're lactose intolerant.
Lactose is basically a type of natural sugar found in milk in most mammals including humans and some people are just intolerant to that.
Lactose intolerance is not as serious as a regular dairy or milk allergy but the lactose intolerance can cause stomach pain, bloating etc.
When you're lactose intolerant your body has a harder time digesting the lactose or sugar found in the milk and dairy products which makes your stomach hurt.
Symptoms of Lactose Intolerance are stomach pain, farting, bloating, gas buildup in your stomach and abdominal cramping.