You could try one of the non-opioid drugs used for neuropathic pain, though these may not be as effective as opioids and some may have a component causing dependence. It would be discuss this in detail with your treating doctor.
Hope this is helpful.
I was diagnosed with IC 3 years ago, and take a nerve pain killer for another condition that I've heard prescribed for IC - neurontin- it doesn't help for me, neither do the anti seizure pills I've taken for migraines. You might try a partial agonist opiate, like tramadol, partial agonists make addiction much less likely, but, of course, are no where near as potent. You can find a lot of info about partial agonists and how they work on Wikipedia, of all places !