The painful tailbone is terrible!! I have CI, and haven't had surgery yet, but had a horrible, painful tailbone for almost 18 months. It may not be related to your surgery. If your google "painful tailbone" you'll get the medical term. I even had my tailbone xrayed because I was sure I had broken it!
I didn't do anything to hurt it, probably just sitting at the computer too long. The doctor told me it takes a LONG time to heal, and then one day it just won't hurt anymore. That is exactly what happened! He said there's no real reason you get it, and no idea of when it might go away.
You can buy one of those special pillows with a cut out for your rear end at some drug stores, and definitely can find them online. The do help when you're sitting watching tv or at the PC, but standing feels much better than sitting. It even hurt to roll over in bed.
Good luck, and hopefully yours won't last as long as mine did.