Sprain of bruise. You might have bruised the pirifmis muscle or the gluteus maximus or minimus. Also, you ould traumatically injured your ischeal gluteal bursa, causing traumatic bursitis. Of course tailbone injuries are possible, but your problem should most likely improve within 2 weeks. I'd take Aleve (naproxen) two times daily. If the pain does not get better, see your doctor.