550 cc HP round sillicone dual plane mentor, with IMF displacement, is this the right choice? Please help! (Photo)

I am sorry to hear about/see the problems you are having after breast augmentation surgery. I think your concerns are appropriate; your breast implants do seem to sit quite low on your chest wall, consistent with breast implant displacement ("bottoming out”).
It is possible that you are feeling the implants significantly along the lower poles of the breasts. Patients in your situation often complain of discomfort in the area of implant malposition. Also, consistent with the breast implant positioning problem, the nipple areola complexes seem to be sitting relatively high, because the breast implants have settled too low. 
Generally, signs of breast implant bottoming out include: 
1. Breast implant "sits" too low on the chest wall.
2.  Excessive palpability or visibility of the breast implant along the lower breast pole.
3.  Nipple/areola complex seems to be sitting relatively high, because the breast implants have settled too low. 
4. Discomfort along the lower breast pole (secondary to pressure from the underlying implant).
5. Relative paucity of upper pole breast implant volume compared to lower pole volume.
6. Increased visibility of infra mammary fold scar (higher on the breast mound).
I think that you will benefit from revisionary breast surgery which will likely involve capsulorraphy ( internal suture repair). Sometimes, depending mainly on the patient's history and physical examination, I will also use additional supportive materials such as acellular dermal matrix or biosynthetic mesh. This procedure serves to reconstruct the lower poles of the breasts and prevent migration of the breast implants too far inferiorly. Associated issues with positioning of nipple/areola complexes and visibility of the inframmammary fold scars should improve with this operation.I find that it is often possible to "go bigger", assuming a well executed capsulorraphy procedure.  In my hands, this is best done utilizing a two layer permanent suture repair. The size of breast implants is then determined based on careful preop communication of patients' goals,  careful intraoperative measurements, and after the use of temporary intraoperative sizers.   The utilization of a larger breast implant helps to achieve the increased upper pole fullness that many patients desire.
 
  Success rates associated with this type of revisionary surgery are very high, assuming  significant surgeon experience, a well executed procedure, and careful attention to postoperative activity limitations.
I hope this helps.

Since you already have fold issues, you are probably best of not putting in larger,heavier implants. This may cause early descent and failure of your capsule repair.   When treating this issue, I usually use smaller implants or a similar size to the one that was originally placed.