You've been through so much, with all the illnesses on top of the TKR, and I think that your body has just lost a lot of condition because of it.
I'm wondering if applying heat might help your muscles to relax a bit. (wheat bags/warm pads/hot water bottles - although be careful not to have them too hot) It's worth a try and you lose nothing if it doesn't work.
Maybe, as your general health improves, your muscles will recover as well. It could be that this takes a while, so you'll need to be patient with yourself.
It must be so frustrating to hear of others doing so well, when they had their TKRs at the same time as you.

Do remember, though, that none of them had the repeated UTIs and the shingles to deal with. I remember when my mother had shingles and it was quite debilitating for her.
BoneSmart is here for you, just as much as for someone who had their TKR yesterday. We'll try to help, for as long as you need us. even if we can't always offer a solution, we will listen with a sympathetic ear.
By the way, Josephine is having a shoulder reconstruction on Monday, 1st August.