Are you sure this weekend there wasn't some other issue, like bloating from TOM or sodium or..?
I really can't see how exercise would directly affect the appearance of your face.. weight loss due to exercise, yes, but it doesn't make much sense to me otherwise that working out your body would make your face appear more sculpted. (Please anyone correct me if I'm wrong)
Maybe it also could be perspective, perhaps the recent 10 lb is showing more in your shoulders and collarbones and makes your face look heavier by comparison.
You also mentioned the previous photos were from summer, could it be you had a suntan in those pictures? Sun-darkened skin can have the illusion of looking slimmer than whatever the natural shade is, I believe.
Just some ideas!