Out of shape?  Were never in shape?
Now’s the time to change all that. But you need to do it intelligently and not hurt yourself. I don’t mean minor discomfort, though it might cause major inconvenience when you have difficulty holding even a coffee cup! Clearly a sign that you’ve overdone things, but nothing actually that bad. No, you need to watch out for sharp pain, and persistent discomfort that lasts over two weeks of rest.
These kinds of pains are complicated matters, well beyond the scope of this short introduction. But …