How can you tell if your kitty broke her tail?

My kitty does not want me to touch her lower backside, she growls and cries. I dont know how she got injured, she is strictly an indoor cat. She is not walking funny, although she walks very carefully.She eats and drinks fine. I have not seen any poop around her rectum, and she is going in the litter box. She cannot jump very well, but I have kept her from doing it alltogether. I touched her ears to see if they were hot from a fever, they are warm. I am wondering if anyone else has had this similar situation. I am afraid of the vet charges because I know they are expensive..can anyone help?