urethritis with unknown cause

[chrisgoring]

  I had unprotected oral sex in late june.  Exactly 1 week later I had clear discharge, urgency, and urethral irritation occur.  I was treated with cefixime and azithromycin to rule out gonorrhea and chlamydia.  Urinalysis was negative for all major std's.  No lesions by the way.  The discharge went away in about 5 days but the urethral pain persisted.  I had a urethral swab in which afterwards, the urethral pain decreased substantially, but was still present.  cultures were negative, but was treated with doxycycline to make sure.  1st urinalysis was clouded with crystals so I went to a urologist to check for stones.  Ultrasound was clear, received another urethral swab, and the pain in my urethra came back to its prior severity.  All in all all cultures are negative and urinalysis.  I have persistent pain in my urethra, and no one seems to know what's wrong. Help!