I think I might have a tooth abscess, but my rhinoplasty is scheduled in 3 weeks. What should I do?

It is not absolutely necessary to reschedule your rhinoplasty. Yes, you should take of your tooth immediately. If your infection clears within a week or so and you take enough antibiotics preoperatively to clear the infection you can proceed with the surgery. If the infection is not under control according to your dentist and your plastic surgeon you will need to reschedule the surgery. 

Having an active infection around the time of surgery puts you at risk for a postoperative infection at your surgical site. First, you need to see a dentist to help you with this AND you need to let your surgeon know about this. I agree with my colleagues that the best course of action is to delay surgery until your dental infection is fully resolved. Best of luck.

Thank you for you question.  Your concern is not misplaced.  It is important that you have your dental issue resolved prior to elective surgery.  Having an active dental infection places you at undue increased risk of post-operative complications.  Make sure you see someone for this as soon as possible and if needed, reschedule your surgery.  Get better!