Severe skin flare up 13 days post rhinoplasty?

Without photos, it is difficult to tell if this is acne or allergic reaction.  Typically allergic reaction would begin sooner, possibly within a day or so of splint and adhesive application.  Since the rash has developed to the forehead (where I presume you did not have any bandages) it may simply be an acne breakout.  I suggest you contact your surgeons office for further evaluation of the adhesives, tapes, etc they used with the surgery, etc to try to track down the issue.