Many dropouts have limiting screws to position the wheel properly every time (push the wheel axle in the dropouts till you hits the limiting screws and tighten the QR)
Make sure the limiting screw is set properly on the left side.
When the wheel shifts to the left it is because the right side of the hub slides forward. The limit screws are just mounting guides - they have no effect on whether the wheel moves after mounting unless it is a rear facing dropout.