Welcome to the STD forum. I'll try to help.
I doubt you have (or had) either an STD or prostatitis. The most common explanation for symptoms like yours, especially when they persiste despite azithromycin and doxycycline, is genitally focused anxiety. If that is the explanation, there could still be a prostate link. The chronic pelvic pain syndrome in men used to be classified as a form of non-bacterial prostatitis -- however, the prostate may not be involved at all, and one theory about CPPS is that it is largely if not entirely an anxiety phenomenon, related to tension in the pelvic muscles. I encourage you to google CPPS (spell it out) and start your reading with the excellent Wikipedia article and information from the Stanford Univ dept of urology, both of which will be near the top of the google hit list. You will find a lot of parallels between your symptoms and those of CPPS.
Besides your symptoms etc, you had an exposure that was very low risk for all STDs. Not completely risk free, but oral sex is generally considered safe sex because of the zero or near-zero chance for some STDs (HIV, hepatitis, chlamydia, HPV) and low risk for others (gonorrhea, herpes, syphilis, nongonococcal urethritis [NGU]). And none of those causes the symptoms you describe anyway. The one that comes closest is NGU, can be easily confused with prostatitis -- but not in cases that don't respond to doxy or azithromycin.
As for clear or semen-like urethral discharge with bowel movements, that's not abnormal. See this thread, as well as the others it links to:
http://www.medhelp.org/posts/STDs/Discharge-and-Bowell-Movement-and-Concern/show/859854
So my belief is that your symptoms are not due to any infection from the oral sex event. If they are related to that experience, it is probably connected with your self-diagnosed anxiety about the event.
Perhaps most important, you can be certain you have nothing harmful. Even if you actually have NGU or a prostate gland problem, these are believed to be entirely harmless when the standard STDs have been excluded. There are few if any long term complications or health problems of any kind, either for affected men or their sex partners. Many men with such symptoms find them quite easy to live with, once they are confident they are an inconvenience only, not an important health threat.
So my advice is to stop testing for STDs; read up on CPPS; then consider visiting a urologist, if you haven't done so, to confirm the diagnosis and get personalized advice about it. But in the meantime, you really should not be worried.
I hope this helps. Best wishes-- HHH, MD