I've had IC for pretty much my entire life. I'm a new nurse but have been dealing with IC for many years, at many jobs as well as in school, so here's my advice for you:
If you don't have an awesome urologist who is well-versed in IC, find one. Most uro's I've known either have no idea what IC is, or have heard of it but don't really understand it. You need to find a doctor who is knowledgeable and sympathetic, so if your doctor isn't, please keep searching.
Get an official letter from your uro stating that you have a chronic condition that necessitates frequent bathroom breaks. (I had to get such a letter in nursing school
because we weren't allowed to take breaks during tests, and obviously that was not an option for me!)
My IC is much milder these days than it used to be, so I manage it through diet and drinking lots of water to keep my urine diluted. Some people have success with the medications Elmiron and Cystoprotek, and there are also Prelief tablets you can take with food that sometimes help reduce diet-related flares. Cold compresses can help too (though it's not especially convenient to hold a cold pack to your crotch at work...) as well as good old relaxation exercises. Some uro's recommend instillations of lidocaine or other meds, though I've never tried this myself as I don't think the pain of catheterization is worth the brief benefits. There's also Elavil and other tricyclic antidepressants for the pain, though the side effects have kept me away from trying that route.
Don't let anyone bully you around about your pain. IC is a silent disease, so while you may look fine from the outside, you know how much you are suffering. It's legitimate and depressing and you should feel free to tell
your employers and co-workers that you need certian accommodations in order to do your job effectively. It sounds like your IC is quite severe right now, but know that remissions do happen, and treatment can make a huge difference.
Check out http://www.ic-network.com/
if you haven't already; sometimes it really helps just to talk to other people who understand what you're feeling. Best of luck and I hope you can return to work soon.