My 9 year old golden retriever, Harry has something wrong with his hip, He seems to have trouble sitting down and whines like crazy. His left hind leg is all stiff And he can't bend it. he is also acting very weird, he walks around in circles and doesn't come when we call him, he also ignores our schipperkie, Taz when he usually plays with him. Please help, what's wrong with him? Thanks in advance.