My recommendation...a good spinal doc; preferrably and OSS along with a GOOD Urogyn and even a spinal PM. I have written before a few times and grant you I don't have stress fractures. I do have a fractured coccyx and minor prolapses. But between my PM and Urogyn they have pretty much sorted it out. And, yes, I know...my issues are different. But the sit pain can be awful! But since you are speaking of the sacrum, illium, sacroilliac joint, and bladder. These are the docs I would see. Oops, I did want to mention the bladder. My prolapses are actually minor and are a cystocele and rectocele. The thing I found out later is that if they were to do the repairs, they would attach the sling at the sacrum! And that is precisely where I have nerve damage or lumbar/sacral pain. So, I am holding off and doing pelvic floor PT to release spasms caused by the nerve damage. So far so good because the prolapses are actually being helped by this. And it will be injections for the coccyx because it has been recommended to NEVER have that removed. I wish I could be of more help.