I can't give you any medical advice--but it sounds to me as if you've got a really really bad fissure. Fissures can be unbelievably painful. (I know, I've had one for the past five years, and my colorectal surgeon has tried everything, but now tells me that it will never heal.) For example, the pain is occasionally so bad that I'm afraid it's an abscess. My husband had an anal fissure (unrelated to IBD), and he spent weeks rolling around on the floor, popping my hydrocodone pills, unable to sit or stand or walk without pain. A bad fissure would explain both the pain and the bright red blood.
That's just my guess, of course. There are probably other things it could be, but I can't think of anything that fits quite as well.
While you're deciding whether to go to the ER or wait until your appointment on Tuesday, try taking several warm baths a day (or sitzbaths, if you can manage them instead) and some extra-strength Tylenol (since aspirin and ibuprofen aren't safe for anyone with Crohn's).
Good luck. Let us know what it turns out to be, ok? I really hope that you feel much better soon.