Scale doesn't tell the whole story-

There are two types of tissue that make up your weight. These tissues are fat and muscle. When you initially step on your scale after a couple weeks of weight training, it may appear that you are losing only about a pound a week or you might be gaining weight. The weight scale does not accurately represent what is taking place in your body. Muscle is a highly active, dense, tissue that weighs more then fat and additionally takes up 5 times less space.

Strength training in essence helps you lose fat / weight or in other words, decreases your body fat, while increasing your lean body mass (LBM). Lean Body Mass is the amount of muscle your body is composed of without fat. Just because you are not losing a significant amount of weight doesn't mean you are not on your way to having a better body. Just pay attention to how your clothes fit. If you are training properly, they should feel loose.

A good analogy to help you understand muscle weight versus fat weight is if you were to compare a soft ball to a beach ball. A softball (muscle) is heavier, yet significantly smaller. A beach ball (fat) is lighter, but noticebly bigger.