Thanks for your query.
From description it seems to be bruised tailbone. You need an x-ray to rule out any bony injury
. Do hot fomentation over sacrum
. It will take weeks to months to subside.
Use ring cushion and take sitz bath [sitting in lukewarm water for 10 min]
like nucoxia 90 once daily after consulting with your doctor.
I do hope that you have found something helpful and I will be glad to answer any further query.