Hey Geordiecat,
First of all, poor you. It's absolutely fucking horrible. I was just the same as you when mine all kicked off - that horrible feeling of needing to wee CONSTANTLY. Was getting up every hour in the night, knackered, scared and miserable.
So ok, the first thing to say is that I'm feeling so, so much better. Up now once a night, if at all; have been to the loo I think three times today. Still a bit more sensation than I'd like, but working on that - rarely feel any pain. It's taken me six months of work, but I have been improving all the time.
The first thing to do is to look at your diet - cut out ANY potential irritants - caffeine, alcohol, acidic food, anything spicy. No fruit juices If you smoke, stop (terrible for bladders). At first, I'd drink only water, to be honest, and stick to Evian (high pH, and low potassium, which can be an irritant). And drink LOTS - 2l a day (don't get tricked into drinking too little to avoid needing to go to the loo). As an immediate sticking plaster, you can try a tsp of baking soda in water, to calm things down.
Take paracetamol for the pain; that's the least bladder-irritating painkiller.
Use a hot water bottle on your stomach and between your legs to soothe and calm everything.
Then I'd also recommend taking herbal baths: a big handful of baking soda, in nice hot water, plus some essential oils (couple of drops of tea tree to kill any bacteria; some lavender or something else that relaxes you).
Hopefully, this should calm things to the point where you can get some sleep.
After that, there are various strategies you can use.
You need to consider whether you want to go for a cystoscopy (camera in bladder) to confirm your diagnosis (and of course you should see your gp to rule anything else out). There are various drugs drs can now prescribe for IC, so obviously that's one route.
However, I think most of us on here who've had results have gone down the alternative/complementary route - basically, it's v poorly understood, but it seems to be the case that IC is a systemic thing, rather than just a bladder problem, and therefore needs to be treated holistically.
I've been seeing a superb acupuncturist, Toni Tucker, who specialises in IC - but she's in Maidenhead, and I'm guessing from your name that you're not? (I'm from Newcastle btw, tho living in London now - hello!). She has people who travel from all over (even abroad) to see her, but realise this may not be an option! Whereabouts are you?
Also, I've been seeing a herbalist, and decided that in my case (it's different for everyone) one of the root causes is a yeast overgrowth (take this quiz to see if it might be an issue for you www.mall-net.com/cgibin/quiz4.cgi?quiz=crook.qa). I've been on a super-strict diet since January, and it seems to have helped hugely. I can give you more details if you like.
Must go now as have been working all evening and need to sleep before starting again in the morning
, but I'll check back in then. You're not alone and we'll all help work out what the issue is for you and what muight work. It's just a case of trying things until you find what works for you.
Good luck for some sleep tonight 
oh and regulars: good news! NOT PREGNANT! the blessed relief 
and cabbage, just seen your PM, will reply tomorrow!
xx