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

Thank you for your question and photo.  Most likely at 3 weeks post op your not having skin necrosis.  An in person examination is needed for a full assessment.  It looks like you may have an early skin infection caused by removal of the rejected suture. This is not uncommon.  Continue your antibiotics and continue close follow up with your surgeon.  Best Wishes

Thanks for sharing your concerns with us. It doesnt seem like you have a necrotic area. I recommend you to perform local wound care with an antibacterrial soap and to maintain the wounds dry and clean. Also, In my practice, after performing a breast augmentation I recommend to my patients to limit the movement of the arms for two weeks. After that, you can move your arms taking care and always with common sense. In this regard, it's not advisable to carry heavy weights to prevent the implant out of position, and allow the formation of the physiological capsule around the implant, also to avoid pain and breast swelling.Respectfully, Dr. Emmanuel Mallol.- 

This area is not necrotic and does not look like it will become so.  You may have superficial cellulitis, i.e., a skin infection and oral antibiotics for a week along with topical antibiotic ointment should resolve this.  

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.