Wow, so first of all, you have been on a lot of antibiotics - none of which actually treat or cure an STD, at least the ones you've named.
Secondly, testing you for an STD while you are on or recently took an antibiotic can give you a false negative result.
However, how long have you been with your girlfriend? How likely is it that she has an undetected anal STD? Have you had anal sex with her in the past?
If your urologist thought you had an infection in your prostate, did he do a prostate exam? Any imaging?
At this point, I think I would wait for 2-3 weeks after you are off all antibiotics and do urine testing for STDs, have it cultured for other bacteria like E.Coli, and do some imaging - like an ultrasound - of the area.
Does your girlfriend know you are going through all this? It would be very easy for her to get tested for STDs while you wait. She could get vaginal/urine testing done, and anal swabs done, too. If she's negative, that would help narrow down your answers.