For what it's worth, I was diagnosed with IC 10 years ago. I was frustrated for 2 years worth of being sent from doctor to doctor who were interested in only giving me drugs to stem pain, not in treating other symptoms (the one that drove me craziest was the feeling of urgency; it was like having a severe UTI at all times--I couldn't sleep nights for more than a couple minutes and was a complete wreck).
I finally read an article on Vulvodynia--and except for the location of the symptoms, they sounded so similar to the IC symptoms that I became convinced they were related. (I later discovered that over 40% of IC sufferers also have Vulvodynia, so turns out it's true). I went to the doc mentioned in the article, Herschel Melmed in Denver, and told him that I wanted to try his regimen for the IC. He agreed and gave me a pamphlet on foods to eat, what to take, etc. And holy cow, I felt soooo much better in just 1 week! After a few weeks, I felt back to normal. How amazing is that?
So what he has folks do is eat a low-oxalate diet. Turns out some folks don't process oxalic acid correctly; it crystallizes in the body. This can result in kidney stones, or if it doesn't congeal into stones, is then passed through into the bladder and urethra. These are like sharp shards of glass, and irritate the hell out of the lining of your bladder and urethra, which makes your body think it's under attack (like from an infection) so then it attacks--but as there isn't a foreign invader, it just further damages the membranes, then all hell breaks loose.
This is the same for vulvodynia sufferers, except that the irritation is primarily external (turns out that IBS and gout are now being investigated for the same cause). So what he has folks do is avoid high-oxalate foods. Some of the biggest culprits are chocolate (*sob*), coffee, spinach, and parsley. You eat only low-oxalate foods, and to leach the rest of the oxalic acid from your system, you take insane amounts of calcium citrate. He recommends Citrical, and I've had great success with it; I take 6-8 tabs of the highest dosage daily, 2 with each meal. The idea is, as the excess is excreted in your urine, it's taking oxalic acid with it. I also learned that Vitamin C is converted to oxalic acid in some people's bodies, so I stopped taking Vitamin C supplements as well.
The difference it made in my quality of life was incredible; I stopped taking all the prescription meds, and have been largely symptom-free for years now. I do notice that when I cheat and drink lots of coffee or eat "illegal" foods, I notice symptoms again, so increase the Citrical and the amount of water I'm drinking.
I hope this helps you; I figure you'd lose about 10 bucks for a bottle of Citrical plus an hour or two online looking up oxalate content of foods, so it's probably worth a try if you're interested in an alternative therapy. The funny thing is, Dr. Melmed is an MD, not alternative-y at all. He's just a research physician doing studies on this process, and this is what has worked out the best!
I could wear tight clothes again, have sex again, be far away from a bathroom again (well, as far away as my poor, scarred, 1/4 cup bladder will allow, that is!), I lead a normal life now. I urge you to give it a try, even if it just helps your symptoms a little, it's probably worth it.