Belgian hare with a bad back?

By Belgian hare is two years old, hes a gorgeous little boy, he used to binky and sprint around the garden, sooo happily. but recently, he can hardly hop at all? when ever he's sat still he is constantly shuffling his feet under himself in pain trying to get comfy, and when he tries to hop.. he can hop a few yards rather wobbly then drags his back legs along behind him.. :/ its incredibly distressing to watch, i love him so much i dont know what to do. we've taken him to the vets and hes' cost us almost �300 .. (injections to help him cope) and nothing seems to be working.. even after 4 months. i dont know what else i can do. anybody with any advise.. please help me.