“Acidity” in coffee refers to a flavor component, not to the PH scale or any acids that will upset your digestive system.
When we talk about acidity in our coffee descriptions, we’re referring to the pleasant brightness you experience when you take a drink. You’re more likely to find acidity/brightness in African and Central American coffees, or in lighter roasts. Dark roasted coffee will be lower in acidity, since the flavor components that are experienced as brightness get roasted out of the bean.
While you are unlikely to get a stomachache from bright coffees, coffee oils may be a little hard on your system. So, if you’re having trouble with drinking coffee, try a lighter, freshly roasted coffee.