burning after urination and ejaculation

well about 7 months ago i had unprotected oral sex with a girl, 2 days later it started burning. I went to the std clinic and got treated for clymedia and gonahria and also got tested. Those test came back neg. The burning lasted another week then went away.3 months later same thing had unprotected oral sex with the same girl,but she gave me oral for a longer time. And two days later same thing started burning after urination. SO went and got treated and tested for stds all came back neg. The doc did a microscope examination with a swap and said there was bacteria. she gave me antibiotics and nothing happend.2 weeks later i went and saw a MD he gave me a uti test that came back neg. He also gave me cipro and nothing happend. I went back to the MD and he gave me bactim, Im on my last day and still nothing.It starts burning after my first urination, If i hold for 2 hours or more it wont burn until i pee or ejaculate. I have no ins and dnt know wat else to do.Can you please help with any suggestions