Is pain classified as medically necessary plastic surgery?

Sorry to read that you are experiencing concerns after your surgery.  Its important to note that you are still in the relatively early stages of your post operative recovery and its important to be patient.  Creaking noises and strange sensations are usually all normal.  Its essential to ease gently back into you regular routines and its usually normal to have some limitations as you ease back into things.  You should not be in constant pain and if it doesn’t resolve than its best to undergo further investigation such as imaging to rule out any concerns. Keep your surgeon advised about your progress and discuss your concerns.  You surgeon will determine if revision surgery is medically necessary and allocate Medicare numbers for claiming rebates.

I am sorry that you are having issues about your procedure and thanks for sharing your question. I can appreciate your concern.
It is difficult to determine the source of your problems without proper examination and testing. The revision surgery would be difficult to have it covered by insurance. however, if you have an infection or bleeding, you may have coverage of the threatening condition but not the replacing implant. 
If you adquired implants extra insurance, sometimes there is coverage of surgery with implant replacement when experiencing capsular contracture.
Finally, make sure that your doctor is aware of your process. He should be able to guide you best in your care.
Wishing you the best in your journey