i have a 6 month old kitten and he has seemed to start whining a lot and sitting in a weird position where he sticks his butt in the air...i don't know what to do or if i should take him to a vet..why is he doing this? my neighbor who owns many cats came over and my kitten hissed at him. My cat has never done that. his mood has changed a lot . i dont know what to do please help me