Yeah, you're definitely not alone there. I'm in Australia and our system here is pitifully slow as well (unless you're in a private fund and willing to pay). But there's not much else you can do except carry on with it and hope for the best.
It's terrible being in pain every day and having to eat only certain things to get by, but until they can nail down what's causing the issues there's not much choice. But on the bright side, they've at least found out definitively what's causing your problem and what steps need to be taken to getting it fixed.
I recommend just sticking to the plainer foods for the moment, things that won't demand a large amount of bile to digest and minimise your discomfort. I've noticed over the last couple nights I'm getting symptoms similar to a gall bladder attack after eating a larger meal, so I suspect I might have the same thing as you
That said, Gall Bladder attacks are a horrible thing to have and I remember them well even this amount of time afterwards. The good news is, once they clear the blockage the symptoms will go away. I remember vividly how different I felt post operation and your proceedure should be even simpler than that (I have a big scar across my belly to remind me of mine!).
Your proceedure is basically an Endoscopy with a little extra thrown in that shouldn't be too bad in comparison (although it does sound frightening). I actually had an Endoscopy done last month and whilst I can't say it was a comfortable proceedure, it's over fairly quickly. You will be awake for it, but sedated and you actually won't remember much once it's done either. But given either that or cutting you open, I'd take the ERCP any day of the week, especially since the results will be much more immediate.
Seriously, whilst I know you're scarred (I know I was before I had mine), you'll get through it before you know it and afterwards you'll wonder what you were so worried about.
Who knows, I may have to go for one myself soon!