Look at the process
Your uterus is about the size of a pear, and it stretched out to the size of a basketball.
At delivery, the outlet, which is the size of a coke bottle is stretched and torn as a kid with a head bigger than most grapefruit passes through it. You might feel fine, but it takes the body a while to repair all the stretching and tearing. ^ weeks will return most tissues to a stable sate.