Verified answer

you were likely always going to be lactose intolerant, you just sped up the process with so much dairy consumption. Usually it takes several years for people to develop the intolerance.

You can increase sensitivities to things like milk just by eating them, and you probably did (as another answerer wrote) just speed up the process of noticing problems.

I suspect you were always lactose intolerant. Humans aren't really made for drinking milk beyond early childhood, and then we're made to drink human milk which has a different composition than cow's milk. The lactose is usually the problem.

It is possible.

Your body needs to manufacture the enzyme to digest the lactose sugar found in milk. Just because it could make it last week doesn't mean it can make it this week. The cause can be genetic (lots of people can't make the enzyme past infancy, even though they have no symptoms of lactose intolerance), or it could be that you don't have the right nutritioal support to ensure your body has enough "parts" to make enough of the enzymes.

There's no obvious solution here. You may never be able to handle milk again, or you may find that things are ok next month.

switch to whole milk. and only drink small amounts at a time to rebuild your tolerance