After undergoing breast augmentation surgery, there can be complications such as implant displacement. This can happen just from gravity, capsular contracture, muscle pull, or the weight of the implant. The best way to tell if your implant is moving by the direction of your nipple. When the implant is displace high on your chest then your nipple direction would be downward.
This problem can be corrected by revision breast augmentation surgery. Some plastic surgeons, make the pocket around the implant smaller or add tissue such as Alloderm or Strattice to the capsule to keep the implant in place. I would recommend contacting a board certified plastic surgeon to discuss your options.