If you are having problems chunking the ball or hitting it fat, try this. In your backswing keep your left leg braced slightly towards the target. This will prevent you moving or swaying too far to the right during the swing which can move your swing center behind the ball. This can cause you to hit the ground behind the ball. Try and also develop a feeling of hitting down on the ball rather than “sweeping” it off the ground.
Be conscious of preventing shift to the right by the tension in your left knee. You will soon be hitting it clean again. Try to be aware of your left legs role in the swing without paying too much attention to it. It will soon be drilled into your sub conscious and you will do this on autopilot.
Another error which can contribute to hitting it fat is poor shoulder rotation. This is usually caused by inadequate shoulder rotation and lifting of the right shoulder during the backswing. This causes you to return the club face to the ball either too low (fat shot) or too high (thinned shot). Correct shoulder rotation is vital to accurate ball/club contact.
Lastly fat contact can be caused by allowing the left arm to start bending during or before impact with the ball. Be sure to keep it straight until after contact with the ball.
Put all this together and you will not be hitting it fat again.