mooshy
I had this problem for almost 6 months. Three courses of antibiotics and on the loo every five minutes. Never feeling as though I was able to empty my bladder. I was getting demented with it and hardly sleeping either 
The girls on the interstitial cystitis thread suggested that I adjusted my fluids.
Only drink Evian (no tap) water, milk, herbal teas or pear juice. These are the least irritating to your bladder 
Cut out everything else.
I did this and within 24 hours I was getting back to normal!
It turned out that it was ordinary tea that was causing all the problems 
I now only drink redbush tea, water, milk, hardly any fruit juice, hardly any alcohol (wine made it much worse, spirits aren't too bad) and herbal teas.
I'm fine now and have had no problems since.
Things in your diet can also cause intense bladder irritation which leads to chronic infections and constant peeing/not emptying bladder because of spasms.
Please try adjusting your fluids for about a week and see what happens. Honestly, it's saved my life. I was becoming depressed and living on painkillers.