Measure body fat, not body weight. Do not get discouraged if you are attempting to build muscle and you do not see a change in your weight. You can lose fat while you gain muscle, resulting in a weight that does not change. A better indicator is measuring your body fat. If your weight is holding steady (or even increasing) while your fat levels are dropping - you are gaining muscle.
Most people use the same repetition speeds for all their workouts. Try something different the next time you are working out and speed up your repetitions. By using faster lifting speeds, you can actually target and work out diverse muscle fibres, some, which may not get stimulated as often.
Now that you fully understand the different aspects of muscle building a bit better, you should start a routine in your life that will increase the progress you have with muscle building. Information is going to make a big difference in the amount of time that it takes you to reach your goals.