Your symptoms could be from a number of sources. The bladder problems can rarely occur from the spine but that would be unusual. There is the chance you have arachnoiditis from your original disorder or from the surgery. An MRI of your lumbar spine would help to diagnose the presence or absence of intra-canal problems that could cause your bladder symptoms. (See website)
The pain in your sacroiliac region could be from a lack of solid fusion from the prior surgery (pseudoarthrosis), compression of a nerve root, chronic radiculopathy (see website) or even originate from the sacroiliac joint itself (sacroiliac instability). A thorough work-up of your spine could reveal the source of these problems.
By the way- “tailbones” (the coccyx) rarely fracture. These bony segments are connected by ligaments and even though these ligaments can be injured (coccydynia), this is a rare condition.
Dr. Corenman
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.