Medical Mystery - Kidney infection clear but back pain

I am a 35 yr old female suffering from a kidney infection for 3 months.  all clear the urologist and nephrologist say.  i still have the lower back pain and it is constant, not going away.  all urinalysis, blood work, CT Scan, IVP scan, shows clear.  They took my gall bladder out last month.  I'm always have nausea and have lost almost 15 pounds since april.  I don't know what to do.  Why have I had lower back pain since April.  Doctors look at me and put me on medication after medication and nothing is working.  Any alternative options?  I never have back pain unless I have a kidney infection.  I had a renal ultrasound and shows clear.  no stones either.  I have been treated for high blood pressure for 10 years now.  I don't know what to do next.  HELP.