nicolemoo, I have had this issue for some time. I also have issues with lumbar and sacrum. What has helped me is to have a ganglion impar block and pelvic floor PT (in the past) which involved the Levator Ani. As a matter of fact, I had the block done about a month ago and the sit pain/tailbone pain is gone. A donut cushion was a no no for me. What you want in the meantime is a coccyx cushion. And getting a nerve block is worth a try.