OK, I looked it up--Interstitial Cystitis.
First, about your husband. If he thinks it's your duty to service him as often as he likes even if it is painful to you to do so, then he seems like a first class ass to me. That seems like your primary issue. No wonder you don't want to make love more often with him--I'm surprised you're willing to at all, under the circumstances. (BTW, I am a man.)
The relationship issues here seem bigger than the sexual issues, to me.
Now, if you can somehow get past that part with him...There's an old joke that goes something like this:
Wife: Sorry, Honey: the gynecologist says no sex for two weeks.
Husband: Oh yeah? What does your dentist say?
Most men would not be upset if their wife offered to give them oral instead of intercourse sometimes. Also, is all sexual stimulation painful for you, or just penetration? If receiving oral is not painful for you, then the two of you could concentrate more on that and it could still be a mutual thing since you'd both be giving and receiving.
More generally, have you been very detailed and specific to him about what is painful and what isn't? Tell him exactly how (if there is any way) he can stimulate you sexually without causing you pain.