Sorry you haven't gotten any help/suggestions - even more sorry your pet is suffering.
I know nothing about the procedure that was done on your dog, but blood in the ursine raises concern in my mind, surely the vet has some explanation for that other that pain relief.
The symptoms you list do suggest your dog is in pain, but I believe most dogs handle pain rather well, mostly in silence...but I suppose some are more vocal.
I read you to have a Lab (not Lad) if correct 10 years old is sadly in the upper range of life expectancy for most large dogs - so there could be problems unrelated to the surgery going on.
Time has passed, let us know how you struggle is going, I'll be looking for some good news.
This may not be blood in the urine -as such- but bleeding in the vagina from the cervix (from her surgery) By now post-surgical bleeding should have stopped. Though after spay surgery there can be a little blood for up to 48 hours so I heard.
There is another possibility, and that is her kidneys were affected by the bloodstream toxins from Pyometra. I'd get her kidney values checked.
You are right -her symptoms do sound like a dog in pain and discomfort. Paracetamol is a good choice as it does not interfere with blood-clotting, as do some pain killers for dogs. (just in case it's her internal wound which hasn't yet started to clot)
It is just possible that any straining to crouch and poop after her surgery could have irritated the internal surgery-site, and caused a little bleed from it.
I would say keep in touch with your vet about this as they have a duty of care post-surgery, and usually prefer to be informed if there are any worries. If you are in any doubt about anything, call your vet.