holby, it sounds like your heel is slipping up and down inside the shoe. (Maybe you have a narrow heel?) Here are two fixes.
Try lock lacing (also called butterfly lacing). There are several variations of lock lacing. Here's the one I use, although I don't pull the laces as tightly as he does in the video. If the technique in this video doesn't immediately solve the problem, try some variations of lock lacing. The idea is to snug the heel into the back of the shoe.
https://www.youtube.com/watch?v=IijQyX_YCKA
If that doesn't solve the problem, notice if your heel moves up and down a little inside the shoe as you put weight on the shoe. If that happens, it could also be part of the problem. Try putting a 1-2mm layer of crafts felt (or any lightweight material) under the insert in the heel area. That will keep the heel in the up position so it's not able to move up and down.
Occasionally, I've had this problem in a new pair of shoes in the middle of a run. I fixed it by putting a small piece of whatever I had handy under the heel area of the insert to keep the heel in place so it couldn't move inside the shoe. I've used napkins, thin cardboard, whatever and replaced it with crafts felt when I got home.