Hey there, so sorry so many are having bad times.
ilmh - really glad you feel you've pinned it down. I know JUST how you feel- having gone through every manner of illness, NOTHING comes close to that constant need to go to the loo. It takes over your whole head. Just awful. Only thing I can say in consolation is that that's precisely how I felt in October, thought I was basically staring down the barrel of feeling like that forever, and really don't have it now. Not wholly symptom-free, still have some residual bladder pain, but a million miles better than I was. Even if you don't pin down an effective antibiotic (though it does sound as if bacteria is the problem for you) there are options. From what I've read, I'd think the first might be longterm antibiotic therapy. Take a look at the work of this guy: www.moonstar.com/~icickay/fugazzotto.html
he's had lots of success in the US. (ps where are you in the north-east, out of nosey interest? I'm a north-easterner myself (though exiled in London these days!))
Beta, both Deborah and my acupuncture woman have said that leaky gut can be a cause of IC. It can also be treated, seemingly, though it's a long-term thing. Yeast overgrowth can cause it, I gather, when the yeast penetrates and compromises the gut wall. Maybe worth looking into? Glad the prelief is doing its job!!
And Viva, jeez, so sorry you're having a crappy time too. D-mannose sounds like it'd be a really good bet. You can order it from a site called Sweet Cures, based in York. Really really hope it helps. If not, though, there are other options, and we're all here to make sure you find the right one. 