Get your prostate checked, could be prostatitis
Hmm, sometimes doctors and patients alike are buffled when antibiotics don't work.
The reason could be antibiotic resistance, which is more
prevalent nowadays or inadequate/flawed testing
to verify the infectious pathogens are not bacteria.
You need to rule out the possibility of a yeast/fungal infection which may be present in the urethra, or Balanitis,
both of which would get worse with the intake of antibiotics!
Prostatitis, as the other poster mentioned, specially non-bacterial prostatitis, should also be ruled out.
Ask your GP, if s/he can help you with this.
Best wishes,
Niko