vraesolo68,
I'm sorry you are having so much pain, and am amazed that you had given birth three times without pain medication.
I would want an MRi to reimage the fusion and to look for any cause of these muscle spasms. Sometimes those fusions don't hold. Some little slippage of a screw can cause multiple problems in even a perfectly executed fusion. If the injection is epidural or even facet, I'd say imaging first. I hope you find relief.