My cat is acting strange! ?

I have a female cat, she's been fixed and has had all of her shots. She loves going out side and will Meow constantly if I don't let her out. One day I let her out and couldnt find her anywhere, 2 days pass and I start searching for her. I found her under a tree and when she saw me she looked so scared! I had to pick her up because she wouldn't move. When I brought her in she hid behind a book shelf for a day and wouldn't even come out to eat! I finally had to pick her up and she went back to hiding. She has a big cut on her ear and walks with her butt down and tail sagging. What's wrong with her? She seems so scared.