It is really difficult to gain 7lbs of muscle- especially if you are a female who doesn't guzzle protein shakes all day. It may be muscle- but for muscle to show through then you have to lose fat. And if you have been working out for a couple of months then your waist and hip measurements are bound to change. Maybe you are putting on weight...what is your diet btw?
Scales cannot determine your body fat percentage- impossible.