The most likly cause is that you have sharpened the cutters shorter on one side than the other, all the cutters must be the same lenght, if this has been going on for some time it will wear the guide bar rail on one side and make it even worse, remove the bar and dress the rails with a file, get both sides as level as you can, now re sharpen the chain to get all the cutters the same lenght, or fit a new chain