Just a side comment...
the water seems to be the issue and the solution.
Doctor exam did not bring about anything either. Funny.. he said pretty much the SAME thing that was said here.
but I notice a difference when she does not get enough fluids.
I have changed her water jug in her lunch box to a larger one and she drains it every day.
Now when she gets up, I wrap her in her blanket and give her something to drink usually water + kids emergen-c package and we drink our 'coffee' in the morning, offering her a little more before she leaves to school an hour later.
When she gets home, same thing.. greeting her with liquid. It seems to help. A lot..