Signs of Infection After Breast Reduction?

Great question. If anyone ever has this question or concern, do not hesitate to call your surgeon and ask for help. Infection usually presents at least a week after surgery, and shows redness that is expanding, pain, possibly drainage of tissue, or increased swelling. If any of these signs are present, it could be secondary to infection and should be evaluated. You may very well need antibiotics and potentially incision and drainage.
-Dr. David Mattos, New York Plastic Surgical Group

Basically, anything with an acute change such as you are describing which is getting larger in circumference should be evaluated.  The symptoms and findings you describe with tenderness, warmth to touch, swelling, and redness are all classic findings diagnostic with infection.  You have to consider it this until proven otherwise, and if you follow that logic, it should be treated immediately.