Prostatitis can be difficult to treat.
The bactrim wouldn't have cured gonorrhea or chlamydia, but it might have inhibited the growth of it enough to alter a test result. However, even if it did, you received the correct medication, and it would have subsequently been cured.
I think you need to follow up with your urologist, and you might want to google chronic pelvic pain in men and you will find all kinds of good info about prostatitis.
AJ
Bactrim is not an effective treatment for either gonorrhea or Chlamydia, thus it should not have interfered with any testing you had done. Your sexual contact was protected and you are at almost no risk for STd`s. Your symptoms are consistent with NGU or prostatitis. Irecommend a follow up with your urologist. Remember, prostatitis can be difficult to treat. Take care
I doubt you contracted chlamydia or gonorrhea from the encounter you describe. You had protected vaginal intercourse--of course this isn't zero risk, but condoms greatly reduce the chance you will acquire an STD, especially the two you are concerned about. In any case, this doesen't sound like a typical symptom for an STD, especially without discharge. If you had chlamydia, the Zithromax would have cleared it up. If your problem persists, I would get another opinion and you could always get re-tested for STDS (to ease your mind). I'm not sure about the Bactrim affecting your test results, but I'm sure somebody else on the forum will be able to comment about this and help you better :)
Good luck,
Em