Welcome to the IBS board!
Let me see if I can help answer some of your questions...
No, IBS is not totally food related. A huge percent of IBS is stress related. There are also people out there whose IBS is mainly related to not having a gallbladder. BUT, in order to pinpoint the foods that are most bothersome you can keep a food diary. Or, cut out lactose or gluten (1 at a time) for a couple weeks and see if you feel better. Then reintroduce them (1 at a time) and see if you symptoms get worse.
There are very few meds specifically for IBS. First there are antispasmodics, such as Bentyl, Levsin and Donnatal. There is also Zelnorm for IBS-C (primarily constipation). Docs sometimes try antidepressants as well, such as Elavil, Zoloft, Paxil and Wellbutrin, just to name a few. You will also find a few OTC meds like Digestive Advantage, probiotics, calcium, Imodium, peppermint oil, fiber, laxatives, stool softeners and calcium.
If lactose isn't your issue you might think about
cutting gluten. Your doc can test you for Celiacs or a wheat intolerance.
Mucus is actually a common symptom of IBS. I don't know much about
UC, but my guess is if you're seeing any blood at all or are having lots of pain that doesn't go away after a BM, it would be the UC and not IBS.
It must be really tough differentiating the 2... I'm so sorry you have to deal with both. I hope I have helped you at least a little bit with the IBS part.