Do my breast implants move to the side too much? Is the pocket too big? (photos added)

Thank you for the question.
 You demonstrate your concerns nicely. Although some “falling to these sides” of breast implants is quite normal when you lie down, if this occurs “excessively”, it may be a concern to patients.  This phenomenon is called lateral displacement of the breast implant;  it may be of concern from the visual and the discomfort standpoints. Surgical correction is an option.
Generally, the lateral breast implant displacement can be corrected using an internal suture technique, decreasing the size of the pockets and moving the implants toward the midline.   In my practice, I use a 2 layered suture technique (capsulorraphy) to close off the space laterally (towards the axilla). The use of acellular dermal matrix is an option (although not usually necessary) especially if significant implant rippling/palpability is present.
 Surgeon experience level and technical expertise play the biggest role when it comes to successful  outcomes with this type of revisionary breast surgery.   Careful attention to postoperative activity limitations as well as use of appropriate postoperative support of dressing/garments are also important.
 I hope this helps.

Dear cristina.93.,
I get this problem all of the time.  Typically, its from women who went with high profile implants.  This is a problem because while they project more, they are narrow at the base and can have widening effect on cleavage.  The second most common problem is incomplete release of the pectoralis muscle medially or wider implant pocket. Many surgeons don't take the time to make this right.  If you're not happy with your results I would suggest you to discuss it with your plastic surgeon. 
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Thanks for writing,Natural breast have some movement laterally, but too much movement and the implants can be in your armpits or on the side of your chest wall, not to mention moving down your chest wall. These things can be fixed, but the goal is to care for them so that is not necessary. The answer is: an anti-gravitational device which you wear as much a possible to help support and control their position. The device is a bra! Gravity is not our friend. Good luck Stephen M. Davis, MD, FACS
Certified: American Board of Plastic Surgery
Member: American Society for Aesthetic Plastic Surgery 
Member: American Society of Plastic Surgeons 
Member: RealSelf Hall of Fame