If you always lift the same amount of weight for the same number of repetitions, your body can obviously handle the stress. Therefore, it will make no changes since it doesn't need to change. If you increase the demands placed on your body, it will respond in turn. As you increase the amount of weight, you force the muscles to develop strength and eventually some size. You are developing your body to your potential.
All women have different genetic potentials.
Set concrete goals for yourself. Consistently training with a high intensity is the only way your body will adapt and therefore change. One hard workout once or twice a month is not enough to create change. It's also not enough to keep you from getting sore, really sore all the time. I tend to get sore after most workouts.