I do not have answers for you about your condition, but I have suggestions....
Get a second opinion if at all possible. There are lots of different meds and other treatments for urological problems, don't give up!!!
Also, what tests have they done? I really hope they have done more than just checking for infection, etc. They need to figure out what the cause is.
Can you empty your bladder all the way when you do pee? Have they talked to you about the possibility of urinary retention or over active bladder?
I had really bad bladder problems for my entire life, and didn't find out until age 20 that for me, it was caused by nerve damage from Spina Bifida. I had been told the problems were all in my head and that I could stop the problems if I wanted to. Luckily, I found a supportive urologist who figured everything out and then referred me to my current urologist. Not at all saying this will happen to you (i have a pretty rare condition/case) but I finally have everything under control with my bladder, after having surgery to enlarge my bladder, using catheters to pee, taking meds, and having 2 different kinds of injections. Sounds like a lot, but my bladder has never been happier! There are so many treatments out there for various problems. I really think you need to find another doc, one that will work a little harder to get you some answers and some relief.
DO NOT GIVE UP!! It may take some time and persistence, but well worth it. You should not have to just "live with it". Let me know if you want to talk or if there's anything I can help with. I look forward to hearing about what you decide to do and what happens.