Emergence of a contour issue months after a facelift suggest a foreign body.
If there is some foreign material in the face placed during a facelift, this might emerge as the swelling that was originally camouflaging it subsides. You really need to contact your own surgeon.
would be helpful to have a photo. A lump under the flap may be from a buried suture. They are often dissolvable, but can create some inflammation under the skin. You should see someone close to you to have them take a look as you may need some antibiotics.