I'd say it's form related, too. If the bow started shooting to one side and the culprit was some change in the bow it would continue to shoot to that side and maybe continue getting worse.

You say you never had this problem before. By any chance did you change bows? If so maybe your new one has more reflex than before. Maybe the draw length isn't set just quite right for you making you vary your form to accomodate it.

I'd play around shortening it and/or lengthening it about 1/4" and see if this helps make you more consistent. If you go this route then give it about a week of shooting to give your body and mind time to adjust.