Well, you may have Gall or Kidney stones. Do you drink alot of milk and/or stay de-hydrated for long periods of time? This may be the cause, and aside from child birth, and being crushed by a tank, its possibly the most painful thing you can endure. Alot of people pass out from the pain.

You can sometimes piss them out, but if their too big you cant. They are probably travelling down out from the kidney into the tubes.

I'd go to the doctor NOW, and get it sorted, fuck health insurance, you NEED to get it checked out.

Im serious.