Yeah - my bladder has like little ulcers in it, so anything acidic irritates it and I will pee constantly. And chocolate is very acidic.
If anyone is interested, there is a vegan "milk" chocolate made with rice milk. I've not tried it myself, but it sure looks good, especially if you don't like dark chocolate. It's called Ricemilk Choco, I think it's made by Terra Nostro or something like that.