I think I don't have a bad back.
That's good. Why say that?
I don't want to hear people asking me why I have a bad back.
It's good people are concerned. Don't pretend to not  have a problem you do.
I'm done with your strict rules. I am going to do what I want.
It can be annoying to have people checking up on you but you shouldn't pretend that you don't have a bad back. You could get in serious trouble if they believe and then something happens and they don't know enough to help you.