#3 Reason why you might be gaining weight...

Reason #3: I've been doing hard workouts for weeks. 

On the performance theme, you need to continually improve, which is why workouts get harder as you move through any of Beachbody's programs. It's also why we add resistance (via added weight or gravity, as is the case with jumping) to workouts. If you're doing the same workouts at the same intensity constantly, you are not forcing adaptations that lead to changes in your metabolism. This is called a plateau. 

A plateau, technically, isn't gaining weight—it's remaining the same—but a proper diet and exercise program should continually force improvements (in the form of adaptations). Otherwise, your metabolism won't continue to increase, which is the goal of most weight loss programs.

Muscle confusion is a MUST with any training program.  SHOCK the body into responding.  Soreness is one thing but remember that feeling when you could barely stand because your quads, hamstrings and glutes were sore.  I crave that feeling.  It is what I strive for out of each and every one of my workouts.  Change it up and watch your body CHANGE IT UP!