Why is there a hole on one side of my breast and how can it be fixed? (photos)

It appears that the muscle has torn away from your sternum causing this depression and letting the implant settle down more. The lateral pocket can be tightened and fat can be added. I do not know if the muscle can be repaired. Or, you can expand the pocket of the other breast and add fat to the depression. Please discuss this with your surgeon.

It may either be a capsular contracture (if the higher breast is firmer or more tender and the breast started lower and slowly moved upwards) or it may just be that the pectoralis muscle was not fully released at the bottom and the implant did not drop to the proper position.
A revision procedure should fix these issues.
The opposite breast with the medial deformity may be either your natural anatomy of may require a slight release to round out the cleavage.
Best wishes.
Dr. Taranow