I fell on my back and butt. nothing is fractured but i have a very sharp spasm on the top of my butt now when i move in certai directions or sit down?

Ideas: How long have you been having symptoms? It kind of sounds like a fracture or bruise of the coccyx. Donut pillows or other padding is the place to start. Avoiding contact the painful area for a few weeks is good, but difficult to do. Take a stool softener to decrease the pain of a hard stool. You could try anti-inflammatory medications and if you don't get better, then you should see a doctor.