Another possibility is that your problem started as a sexually acquired nongonococcal urethritis (NGU). Following oral sex, some NGU probably is the urethra responding to entirely normal oral bacteria, but ones which happen to cause an inflammatory response. Such forms of NGU are generally considered harmless; and although treated with azithromycin or doxycycline when diagnosed, they probably clear up without treatment. Whether this form of NGU should be considered an STD is a matter of professional uncertainty and debate; it isn't caused by any known STD bacteria or virus. However, it is plausible that some such infections might trigger subsequent nonspecific inflammation that explains symptoms like yours. As a sort of similar example, the condition called reactive arthritis occurs as an immunologic reaction following various infections, but is not due to infection per se. Could such a process occur in the genital tract and result in prostatitis? This has not been documented or, to my knowledge, even studied. But there's no way to prove it can't happen. If it does, antibiotics are not likely to help:  they only treat infections, not other kinds of inflammation. In any case, no STD is known to cause the combination of symptoms you now have, whereas prostatitis frequently does so.

Those comments address these questions in general terms. As for your explicit questions:

"Any other antibiotics worth trying?" Various antibiotics (e.g. Bactrim®, ciprofloxacin or related drugs) often are used in prostatitis and may be worth a try -- something to discuss with your urologist.