Is this first time? You must rule out other diagnosis of such pain like infection. If infection is not there, you can simply take analgesics, ice application and do some measures that can help. Use cushion for sitting, available on amazon. Even soft pillow can do the work.
But you must rule out infection (like plinoidal sinus), visit the doctor once.
Next Steps
Visit to the doctor (general surgeon/ orthopedician)
Health Tips
must avoid sitting on hard surfaces in any situation.