I'm a pretty skinny guy and I'm half-Asian (I wonder if genes have anything to do with this...), and I'm 16, and every EVERY time after I drink coffee, like I just drank iced coffee with whipped cream, I'm getting diarrhea. It sucks, it's really bad. Also I get diarrhea sometimes after drinking milk, sometimes dairy products, and a lot of the times, chocolate. I remember when I ate McDonald's after it it cured it, sorta, but what else can I use as a cure?
I might even need to have to go right now, brb