Thanks for your picture. It looks like you have nipple necrosis. There may be infection associated with it but this is only diagnosed with an examination.
Thank you for including a photo. While it's somewhat difficult to tell from your photo whether or not you are having an infection, your symptoms do sound concerning for one, and it's always better to be safe and contact your plastic surgeon to see if he/she recommends a course of oral antibiotics.
From the photo it appears that you have some degree a vascular insufficiency. I recommend you follow up with your plastic surgeon.
Wound healing problems after a breast reduction
Your problem is more due to vascular insufficiency. Continue to follow the advice of your plastic surgeon so that you heal properly.
Do I have an infection in my left nipple? Please advise
You need in person follow up care for this serious post op complication. Local self care is NOT appropriate in this presented case....
Looks like necrosis
Rather than infection the photo looks more like necrosis of the tissue. Proper care by your surgeon with debridement and would care will allow it to heal.