The size of your tummy can change drastically with position. Depending on where your placenta is, his legs might be pushign into that, decreasing your perception of movement.
But of course, if you are worried, call your HCP.
I don't have a son, but nobody in my family (mom or dad's side) is circ'd and I've never heard anyone ever talk about UTIs.
I've had UTI's and I'd prefer that to having a piece of me removed without my consent.
My midwife says she doesn't mention any soft markers to clients.
I had some issues with my daughter's scan- echogenic bowels and some other soft signs of T21 and CF, most of which cleared up by the time we had a sono at 29...
I had one or two prior to birth, and then I had a bunch of them crop up around my navel after the baby was born. They weren't purple or red, just shiny and white from the get-go. I can't see them now.
I have one from this...