What can be done for saggy breast skin & stretch marks that still show after breast lift with implants 3 months post op? (Photo)

You are already bottoming out. I believe it will get worse over next 3 months. Would ask your surgeon to redo the breast lift, reduce the size of areolas, and tighten the inframmary folds. 

The breasts may lose their
elasticity and firmness which can be caused by different factors such as
pregnancy, massive weight loss, lactation and aging. To reaffirm the breasts
and restore the natural look your surgeon can perform a mastopexy or breast
lift. A breast lift restores a firmer, perkier, and more
aesthetically pleasing shape to sagging breasts. This not only can improve
a patient’s appearance by restoring her youthful, feminine proportions,
but also help bras and swimsuits fit more comfortably and attractively. By
removing excess, stretched out skin, reshaping the breast tissue, and raising
the nipple & areola into a more forward position, a cosmetic surgeon can create
a more youthful breast contour. Stretched, large areolae can also be
reduced during breast lift surgery, creating an overall better proportioned,
natural looking breast, Actually the perkiness on a person or another, depends
on patients skin and breast tissue for the first 3 to 4
months! 

are somewhat limited on the trunk/breasts.  If you can't get the desired results with surgery, consider trying ThermiRF that uses probes under the dermis to heat it up and get it to shrink/tighten over a few months.  If you are patient and the surgeon has a reasonable policy in case it doesn't work, its certainly worth trying as it has been shown to provide a little additional lift as well.