5 years post-op breast augmentation - red mark on nipple and it's sore to the touch - advice?

Without more details, it is difficult to provide any specific guidance. You are doing all the right things by seeing your doctor for a full assessment and examination. With all the publicity about textured implants and cancer, I can see why you are concerned. To (maybe) put your mind at ease a little bit, the cancer associated with implants is very rare and tends to create changes to the whole breast, such as breast enlargement, hardening, and pain although there may be more subtle signs like skin rashes. Once again, the first step is to see your doctor, and they would order any further tests or imaging.

You've done the correct thing by scheduling an examination with your surgeon. She/He will advise what is recommended after an evaluation. If an MRI or another test is indicated, your surgeon will let you know.