I've got it again.
When I was around 7 months pregnant with *L* I went to the hospital with excruciating pain in my back. I was hospitalized for 3 days so that they could monitor my pain and give me meds.
Before that I had NEVER heard of 'hydronephrosis of pregnancy'. Apparently it's not unusual, the nurses were all surprised that I hadn't had it with any of my first 3 kids.
Hydronephrosis is explained very well here. Basically the baby is kinking my ureters (the tubes going from kidney to bladder) and that causes my kidney to get backed up. Unfortunately, there's really nothing they can do since it will fix itself after the baby is born.
The things we go through to have kids... :)