Gummy implants typically do not sag and bottom out, but you did choose large implants for your frame. Right now, you are probably fine. If you have more sagging, you should go smaller.
Do remember that you did not like your breasts prior to surgery, so with removal only, you still probably will not be happy. I would suggest going smaller and a moderate profile.
Yes, you large implants are probably the cause of your neck and shoulder pain. At 5'2" and 130 pounds, 520 cc implants are large and heavy. I would suggest going down to around 300 to 350 max.
