Pain in lower back and buttocks can be a sign of nerve compression in the lower back but needs to be confirmed with typical history and examination findings.
Tail bone pain is a different issue altogether and has to be managed separately.
Next Steps
Get a consultation to diagnose the problem.
Till then, Use a Lumbosacral brace for back support.
Use a Doughnut cushion while sitting for tailbone pain.
Apply warm water bags.
Apply pain relief spray.
Video consult with me if pain is too severe.