Mine wasn't overly massive, about 5mm which is about the limit when "peeing them out".
Drink alot more but don't drink fizzy pops and try to limit your salt intake, that's all the doctor said to me but I'm sure google will bring up a fair few other things.
Looked like a small bit of flint ^^
Aaaand yes, ouch! I don't think I want to pee again for a while