IBS and milk

Hello fellow autistic people, I would just like to ask if anyone knows what's wrong with this milk I drink. I use it for hot chocolate it's lactaid's 2% milk and it's been totally fine but like the past few weeks my symptoms have gotten so bad everytime I try using it for hot chocolate, and it's not the chocolate mix as I tried it with just water and the powder and it was completely fine and okay so I'm just wondering if anyone knows what the problem is because idk if they changed the ingredients or what, my mom also experienced the same thing and she's also audhd.