Take it to a good archery shop and have them adjust your string a little. If they can't fix it got to another shop.
I had this same issue just this summer with my new Hoyt. I took it to a different shop then what I bought it from and they told me the d-loop wasn't tied tight enough. Put a new loop on it and I haven't had to turn the peep since. Sent from my DROID RAZR using Tapatalk 2
If you can't do it yourself, go to a good shop and have them help you get your peep adjusted correctly (could need more attention later, depending on your string). Once the peep is adjusted correctly, tie the string loop accordingly. Don't just throw the peep in and expect the loop to cure adjustment problems.
Does it turn as you draw back or is it turned to start and stays in that position while at full draw too?
Had this happen to me as well. I took it to the local shop and put in/took out a 1/2 twist, can't remember, in the string and has been fine since.
A D-loop will self tighten itself with a few draws. If the loop position is off a little, you can use a pair pliers to gently rotate the loop to the proper position. Before performing this function, check to see if the rotation will help to bring you peep into position at full draw. Otherwise, you will have to go to the shop and do as the other's have reccomended.
Depending on the quality of the string, Some strings will continue to twist. A peep with rubber tubing can help in certain situations with that.