unexplained reoccuring fever for over a year

I am running a reoccuring fever every 7 to 14 days.  The day before I have joint pain, always in my hands and feet, but in other joints that change.
I am very on edge so I know the fever will come the next day.  It alway comes during the early morning hours and starts out with hard chills that can last for hours.  I have had blood work ran many times even during the fever.  I have been to the rheumatoid and infectious disease doctors, all came back neg.  I started this in Aug 2009,  So its been happening for over a year.  The fever is wearing me out and I have no energy.  On day when I do feel good  by the afternoon my body just quits, and I have to go to sleep.  If you have any sugestion I would be thankful. I am 51 year old female.  I had a hysterectomy at the age of 40.

[needideas]

I have fever and shills every 12-14 days and no one can figure it out.  I get achy joints the day before an episode.  The infect. disease doctor could not find anything.  I also have bloating/burping so the doctors were focusing on gastro. issues at first.  They did find overgrowth of bacteria in small intestines and treated me for that.  It is interesting that the doctors seem to give up if they know the diagnosis.
By the way, when I get the chills I found jumping into a hot bath can eliminate in seconds.  As soon as I feel the chill starting, I get in the tub rather than waiting. It works like magic.