Oh, I see.  They always told me not to pee before my ultrasounds.  The one I had a couple weeks ago I decided to just cut back on water and drink it later and she still said I was really full, and I definitely wasn't in pain this time until the very end of the ultrasound.  I get that they want to make sure you can see the baby but they should let you know it doesn't have to be THAT extreme.