my german shepherd chases his tail and whines?

[K C]

i have a 9 month old pure bred german shepherd, he chases his tail constantly. its basically all day everyday. sometimes he will whine and than chase it. i try to hold his head and pet him because i seen that it could mean he wants attention but he pulls and crys until he gets his tail. he gets so exausted from chasing his tail and i dont think all that can be good for him... i need some vet answers or someone that has had this problem. i dont want something to be threatening to his life going on so i need to know whats going on