Oh Wendy, by the way...I was just looking at your signature.
Have you not had SI injections before? They are very painful, BUT...for me have been extremely successful! I was getting the Depo Medrol injections in my lower spine for years until that doctor left. A new doc came in and said he wanted to try something different...that often 'they' were finding that the sac joints were causing lower back pain.
They worked small miracles for me. I highly recommend doing that if it's an option.
Now to find a miracle for my tailbone.