One problem for new players is that they have little understanding of what major (or minor) errors they're making in any particular shot. As you improve, you'll start to self-diagnose, i.e. associate certain errors (e.g. pushes, chunks ....) with certain specific swing faults that you know about (e.g. too far inside on the backswing, lack of proper forward weight shift on the downswing).
Be patient. If you keep working on it, this will come.
You'll find that your body naturally finds a consistent posture that works over time, that'll stop the fluctuation in your game. Remember to bear this in mind and keep focused, don't let the frustration of a good/bad day cycle wear you down!