It seems like you are having pain in the tail bone called as cooccydaemia which generally occurs when you fall on the ground or get hurt by something or sitting on hard surface for along time/travelling for long.
Next Steps
Go to a physiotherapist.. Ultrasonic therapy +IFT +Heating therapy +some strengthening exercises will be helpful for sure.
Health Tips
At home.. Rest +hot water fomentation +pain killer gel +use of cooccydaemia ring+avoid hard surface while sitting.