Oh that sucks!! you poor thing, bed rest isnt good.
Can you move much??
I know this is going to sound silly..but i once saw a tv show about a guy that was MAJORLY overweight. He couldnt get out of bed. And he used to clap to get his heart rate up.
Im not saying your THAT big. But i wonder if that might help you?
Anyway, I hope soon all will be better with your back, and then you will drop those KG's
All the best