This is her back in August

and this is her now

I have taken her to the vet who had a good feel around and has found there's nothing obvious and that it is just loose skin. However, I think it's probably a symptom of something else. She's eating, seems happy enough but is shaking her head more than usual I think and just doesn't seem so lively. Also, though she's preening plenty and is very clean and tidy, in the bad weather of late, I think she's not been as waterproof. Any ideas would be gratefully received. Thanks,
Mark