@Denmother
I know you're an athlete and I know that you say you are listening to your body.
However, please think of this:
No matter how fit you were, or how fit you want to be again, your leg has still had the same major surgery that other people's legs have had.
Your leg was cut open, tissues pulled aside, the ends of two large bones sawed off, then large foreign bodies were hammered and cemented into your bones, before all your tissues were put back in place and you were sewn back together.
That created serious trauma to your leg. Your tissues will need time to recover and repair themselves - and that can take as long as a full year. Being fit is not going to make those tissues repair themselves any faster than anyone else's.
It is not advisable to start any strength training before at least 3 months after a TKR. By using 20 pound weights at this stage, you are running a serious risk of not only compromising the healing of your knee, but also causing stress and damage to your back.
Please ease off.