Lactose and tolerant? Please define.?

I get sick when I eat Sonic shakes. & an idea was brought up that I could be somewhat l&t. Drinking chocolate milk upsets my tummy, but I love it. Grilled cheese I don't remember. Bout to find out lol. Last night after 1/2 of a large sonic blast though, diarrhea & vomiting. Any info on l&t? & a connection of this with that?