About 5 weeks ago i had anal sex with my girlfriend for the first time. We used a condom but then switch back to vaginal sex which i know is a big no-no. The condom feel off and we had vaginal sex for about 20 seconds after. Nothing happened for about two weeks and i thought nothing of it.

About 3 weeks ago we had sex and afterwards i had a bad urge to urinate afterwards. I did and it burned on the tip very badly for about 20 minutes and went away. I thougth maybe i just bent it the wrong way or something.

A week after that we had sex again and the same thing happened and the pain was the same type of pain just not as bad . I figured what ever happened is healthing and getting better. This was a Monday and that friday i develop a constant pain in the tip of my penis. Its not very painful but it is very annoying. It comes and goes throughout the day hurting more then not. I went to the doctor's and she tested me for gonnerhea and chlyamedia both came back negative as did the urine test and culture.
She game me Dexycyline for 7 days and said it might be a slight case of Prostatitis. This did not work and i still have the symptoms. I take pyridium and this seams to help but not 100%. I have been with my girlfriend for 2 years now and she was a virgin so i know its probaly not a STD.

My question is what do you think this might be. What should I do?