My cat has a mysterious wound?

i was petting my cat and i noticed she had a cowlick in her fur on her hind leg, near her tail. she growled when i touched it and my fingertips were wet, it was clear fluid, no color. i'm not sure if she was licking it and that's why it was wet, or what ever that sore is has been running and that's what liquid i felt. i put the cat on the counter and she growled when i moved the fur around the wound, like it hurt her. the skin was reddish looking but it didn't look like an open wound. i took a washcloth and touched it to the wound and she howled so i let her go and there was a reddish orange spot on the cloth. what could be wrong? the wound was like the size of an m&m, and the cat hasn't been in any fights to get something like it