First off, you would never gain that much muscle weight in a week. Secondly, how is your diet? Are you consistently eating in a deficit, about 500 calories less than you basal amount?
Also, make sure you are weighing yourself in the same conditions. Ideally, it should be in the morning, after waking up and using the bathroom. My weight can jump up 4-8 pounds just by drinking a lot of water and eating whatever throughout the day...
