Your MD is right, you should see a urologist.
I went through the same thing just before I got married. I was diagnosed with a UTI every month, just days before my period started. Finally the month before I got married I said something to my MD, who thought I was getting them because of sexual activity, which was not the case. Anyway, I went to a uro, and they diagnosed a ureter infection, that would respond to the antibiotics for a little while, then flare back up again during the drop in hormone levels. He told me the symptoms were very similar, and many MD's mistake them for UTI's.
He put me on some different antibiotics and another pill that makes your urine turn bright, bright yellow (can't recall the name, but it's a purplish color. LOL - scientific, huh? :chuckle ) and that took away all the pain associated with it.
My uro and his nurse were just the sweetest. They squeezed me in so I could get treated before my wedding and honeymoon (hint, hint), and even called to make sure I HAD a good honeymoon!
I hope your problem is something as easy, and you can get a quick appt. That kind of pain associated with them just suc#s!