I started having coccyx pain within a few weeks of Noah's birth (only painful after I would sit for a longer period of time, and the pain was when I would rise to standing). Eventually I discovered that my coccyx was no longer curved slightly forward toward my pelvis (the correct position) but is instead pointing straight down toward my feet! Noah was breech and I think he must have pushed it into that position during his birth. The orthopedic doctor who I went to see for help told me it was fused that way and there was nothing to do for it - she actually suggested that I try to FALL DOWN and re-break it!
Anyway, on my own I discovered that it is not fused at all (I can get hold of it and wiggle it back and forth) but still malpositioned. It doesn't bother me that much anymore...if it did, I'd probably find a good spinal physical therapist or maybe even a chiropractor (never been to one before). My only consolation is maybe this new baby will just slide right on past without any trouble... :LOL
I wouldn't think you are doomed to the same injury with your next birth - like pamamidwife said, maybe your baby repositioned it for you! Hopefully things will go better the second time.