A red spot still appear at my nose bridge 3 weeks after rhinoplasty, infection what's the reason? (photo)

Thank you for your question. I suggest that you consult with your board certified facial plastic surgeon because it is important that you and your surgeon review this spot and discuss recovery guidelines.
Best wishes,

If your nasal bridge is just persistently red, without tenderness, it may not be infected. Occasionally prolonged redness may occur on the nasal bridge after rhinoplasty, but this typically clears and may be improved with IPL or other vascular lasers. Consider discussing your concerns with your surgeon or another rhinoplasty specialist. Hope this helps! Dr Joseph

ALthough I do not have all the information about your infection, there is a possibility your surgeon may have used a graft of some type.  In any case, inflammation can last up pto a year or more and redness is a sign inflammation and it should improve over time..  Make sure that your surgeon is aware of your concern.  Good luck!