Why has my internal belly button skin turned white? I’m 3.5 weeks post tummy tuck. (Photo)

Thanks for the question.  Most likely, the whiteness is related to maceration of the belly button tissue.  You may benefit from allowing the tissue to dry out to determine its viability.  See your surgeon to assess the situation.

Thank you for the question.The whiteness may be the consequence of too much moist in the area, try to dry it and keep it clean.Please consult your surgeon for follow upBest wishes
Dr Genevieve F.Caron, Board Certified Plastic Surgeon
Montreal, Canada

Thank you so much for submitting your question. 
It is difficult to assess your issue without a physical examination. To me it looks like you may have a suture abscess though without having done your operation it is a challenge to determine that without knowing which suture material was utilized. I think the nurse is treating the situation appropriately and I think you just need to follow up with your surgeon closely. 
Thank you again.