Intense stomach pains?!? please help me!?

every few months I get these SUPER intense stomach pains, it usually occurs at around 12:00 to 1:30 in the morning (if I'm awake) or if I'm not awake as soon as I wake up. they are really bad and I end up literally screaming in pain on how bad it is. I immediately try to go bathroom and usually end up taking a massive s***, but even after the pain could persist up to an hour and a half. during that hour and a half I'm usually on the toilet s****** my brains out to oblivion. And while I'm s****** to add to it, the pain is nonstop throughout it, I have no clue as to the source of the pain, although I am self diagnosed lactose intolerant, could it be the consumption of too much dairy products? usually I drink lactose free milk but we don't have much money so I sneak regular milk so my mom dosnt have to worry about buying expensive milk all the time. could it be me drinking regular milk? or if you have any other explanations please help me