Sorry guys, just got home from taking my FIL to chemo.
I really don't know what it could be, but I do thing you need to see a good ET nurse or possibly a surgeon (especially if you suspect the stoma is pulling away from the skin), a GI isn't going to be real knowlegeable.
It sounds like a pressure sore, weird place for one, but there it is. I can't imagine it's an allergy, or all your skin under the adhesive would be raw. It may be a leak like Amey said, which caused your skin to get pretty raw.
Is it possible you pulled a layer of skin off when you took your flange off? I've done that, it's usually pretty painful though.
Sorry I can't be more help, and you're right the ER probably won't know what to do. I would hold out to see an ET nurse as long as you can control the bleeding and are able to keep the flange on.
Maybe call your hospital and see if there's another ET available on staff to look at you tomorrow. The hospitals usually have more than one on staff.
Good luck, let us know what happens.