side pain and low grade fever

I've had a really good almost year since my surgery.  My urologist is really positive and encouraging as well.  All blood work and xrays are good.  I'm getting the usual back pain, but has anyone experienced side pain with fever?  It doesn't happen often, every few weeks or so, and I can't associate it with any physical excursion per say.  Only last for a few hours, and I'll be really tired that day.  Normal???  I hate being a nervous nellie!