Suddenly lactose intolerant???

Ally

Does anyone know why I randomly am unable to digest any kind of milk?! Like chocolate or white milk? I used to be able to drink a 2L if I wanted in one sitting I never had problems with it, but the past 3 days anytime I have any milk my stomach cramps a lot and I get loose stools. I have no idea why this suddenly changed after 20 years of LOVING chocolate milk? Is something wrong?