“Bad Breast Surgery”

I got my breast augmented 3 years ago, with saline implants, my breast were not sagging before the surgery I just wanted to have the bigger look, Now 3 years later my breast are sagging real bad and I called my Dr. and he told me that I would need a breast lift and another implant... but the lift will leave me with an unwanted diagonal scar from the bottom of the breast to my areola. Why this happened only 3 years later? Is this normal? I am only 22 Years old, 5"10, 132lbs I went from B to a large C.