I doubt that you gained 5 "real" pounds in two weeks. Anecdotally (n=1) I generally gain weight when I exercise. Some of it is water--I tend to bloat up when I do long cardio sessions. When I slack off a bit, the weight drops immediately.

Be sure you aren't using exercise as an excuse to eat. Like me. :blush: Try not to think "oh, I exercised for an hour so I need this brownie and smoothie and extra slice of pizza. And a beer. Or two."