Is this the beginning of necrosis? Three weeks post off breast implant and lift. (Photo)

Hello dear, thanks for your question and provided information as well.. I have
to say that you are still early on healing process, it is too soon to determine
how your results are going to be, per now, they look very nice and beautiful,
you can have one bigger than the other, it is normal and that can happen for
the first 3 months until your implants have settle in. I recommend you to wait
and keep using your post surgical bra, that will help you with the shape and
support. You're not having any necrosis, Hugs!

First of all, "is this the beginning of necrosis?" Is a question for your surgeon not the Internet.  But, having read the rest of your question, I do think you are on the right track,  it is impossible to say for sure from a picture ( difficult even with an in person exam) but this looks like either inflammation from a suture spit, or early infection.  Either way your doctor has you covered appropriately.  Continue to touch base with your surgeon should anything change.