what are you feeding it , it may not be getting the right food. i had one like this and was feeding it mainly skined rabbit and dry food .
my friend had it for a week when i went on holiday and it came back right as rain.
he said i need to give it some fat and crap from the butchers as rabbits dont have a lot on them which i do now and also an egg once a week and puppy milk which has goats milk in.
i was feeding mine to posh he just chucks a hole gutted rabbit in i now chuck half a one in each time as i only have two jills.
ben