How much weight to gain in muscle?

I just started doing BodyPump which I'm sure some of you know about.  I have gained about 7 pounds though!!!  Is it normal to gain THAT much?  I'm working every body muscle group so maybe it is possible.....its just so discouraging since I'm a slow loser anyways.  Maybe I wont be a slow loser once I build some muscle though.  I'm doing it 3x a week...if that makes a difference.