Hi Christine,
I'm on Day 5 recovery and have had daily muscle spasms in my hip flexors, I think, basically where the OA used to be - on top of my hips and upper thigh. I medicate the '7' level pain spasm down to a '3-4'. I ice, ice, ice, etc., and listen to the nurses who say it's totally normal. It's tight right there from disuse. I was told to try laying flat to stretch it out, do my heel toe and the other gentle in bed 3 PT exercises. It does subside.
My R knee has had a few shooting pains too, but I chalk it up that my body is getting used to having perfect hips after 50 years of genetic malformation. I try to do the chair sitting for 2 hours a day that they started me on in the hospital, and that feels surprisingly good on my tight bilateral hips.
This is completely normal and IMO your body is signalling you that it either wants something different from you or that you are healing nicely and may it have a rest please? I also thinks it helps to rest to medicate pain if it's severe. You'll get better and won't need pain meds anymore soon enough.
I hope to be right there with you when our 'growing pains' are history.