Another thing to consider is, could it be the shooter? Please don't be offended, because something like this was happening to me. I'd shoot a couple of arrows and I'd be hitting consitently to one side. I move the pins a little, pull my arrows fron the target and I'd be shooting the other way, no matter how much or little I moved the pins. Sometimes I'd shoot to one side with 5 arrows, pull them and shoot the same arrows to another point of aim the next five shots, without changing the pins. I wasn't being consistent with my release, anchor point or grip. It took me a while(practice...lots and lots of practice) along with some help from a friend who could see me screwing up and who could fix me without me going upside his head, to fix this.
Have your bow checked over closely, then have someone check YOU(and your form) over closely.
HWD