ok time for my 2 cents (Euro cent that is)
If the OP has already had a lesson and been told the reason for the shanks then we need to address that and not offer any other magic solutions or quick fixes.

My advice to try and stop this reverse pivot is:
1) Take 3/4 swing and aim for a punch shot
2) On your backswing press down with the inside of your right foot
3) start the downswing by pressing down with the inside of ryour left foot
4) swing nice and slowly and dont worry about anything other than this feeling (and of course staying down behind the ball until its gone)

This is the sort of weight shift feeling you want

Try this and let us know how you are getting on...