Implants Don't Lift the Breast
Sagging of the breast can't be corrected with implants, no matter the profile.
If the nipple is below the height of the breast crease, it can be lifted only with a breast lift.
If breast tissue is sitting too low on the chest (below the breast crease), adding implants will simply make the sagging breasts into larger sagging breasts!
High profile implants do provide a rounder shape to the breasts, and more upper pole fullness, but don't elevate any of the tissues.
Your implants aren't sagging - your own tissues are
No implant will lift sagging breast tissues after massive weight loss. Even HP ones! You need a breast lift to reshape the breasts, get more tone in the tissues and to elevate the nipples to a youthful location. Implants will then add volume to the newly shaped breast (can be all done at once). The HP's will give you more projection and upper pole fullness than the moderates but by themselves won't lift your tissues if they are droopy.
Your implant profile is not what is making your breasts sag
It sounds like you need a breast lift. An implant, no matter the size or profile, will not "lift" your breast. You'll need to talk to your surgeon about your expectations and ASK him why he used the implants he used. But don't expect any implant to lift your breasts---let your surgeon know your end goal, then let him tell you how he recommends you get there. Good luck!
Certainly if you are unhappy you should review this with yoru doctor. The sagging of lack of fulness, tightness, whatever, may be related to the quality of your skin after the weight loss. Perhaps you need a breast lift?
Shape of breast implants not the cause of sagging.
Your breasts sag after breast implants. This usually means that you needed a breast lift together with your breast augmentation in the first place. The exact shape of the implants would not make the difference. You might look worse with high profiles.
Have you received the identification documents on your implant type? Every patient is supposed to receive this information for their records. I am a little concerned about the "them" and "they". Sometimes "they", meaning the surgeon's staff don't correctly communicate information, vis a vis, the old game "Telephone" (if you're old enough to remember that). I suggest a follow up appointment with the surgeon. Then you can get the information straight from the horse's mouth. If it's not the information that you anticipated based on your pre surgery discussions, you can have a frank conversation with the surgeon to see where the confusion occurred. Good luck!
You may need a breast lift
I agree with Dr. Yuan that you need to have a frank and open discussion with your doctor. If the wrong implants were placed, then correction is indicated.
That said, breast implants, high profile or other, can only achieve a small amount of breast lift. If your nipple was below the fold beneath your breast (the inframammary fold), then no implant can achieve a lifted look. A dermal mastopexy or breast lift is required to place the nipple in a higher location.
5 months is long enough to achieve a final result in terms of breast implant position. I know it is hard, but try to have a frank, objective discussion with your doctor about your disappointment. Be calm and do not let anger creep into the discussion. Your doctor wants you to be happy and will work with you to resolve the problem, but dont make the doctor feel defensive; that will be non-productive.
Be sure that you ask the doctor if you need a breast lift-if you do, your current implants may look excellent after the lift.
Talk frankly with your surgeon
I feel that most of what is really crucial in plastic surgery happens before you go into the operating room. And the most important thing is communication. If you and your surgeon agreed on a specific procedure with specific implants then someone has some explaining to do. However, often procedures are not worked out in fine detail and much is left to interpretation or to judgment. Ask your surgeon why the implants you thought was going to be used, or that you agreed was going to be used, was not. Some times it is a matter of semantics and labeling since different implant companies use differrent terminology and a doctor can refer to a "moderate" implant that is really a low-profile implant or refer to a "higher" profile implants that is only a mid-profile or moderate plus type implant. In the end, what is used may or may not be important, only whether or not you are satisfied with your result no matter what has been used.