Is It Normal to Have One Nipple Up and One Nipple Down After a Breast Reduction? and How Long Does the Swelling Last?

It is not possible to give you good advice without direct examination or viewing pictures.

At this stage in your recovery, some degree of breast asymmetry is very common (the rule as opposed to the exception). You will find that the breasts will likely change in size, shape, and symmetry for the next several months. I would suggest that you evaluate the  end results of the surgery  approximately 6 months after the procedure.

In the meantime, continue to follow-up with your plastic surgeon who is in the best position to address questions/concerns and rule out complications.

Best wishes.

It is not normal to have uneven nipples following breast reduction surgery, but it is certainly possible it is part of the healing process for you.  It also might be possible that you have pre-existing asymmetry that has been improved with the surgery but is not yet perfect. 

It is too early to know if the swelling is the cause. But if the situation doesn't resolve your plastic surgeon could easily correct the nipple position and any size difference. At this time  follow up with your plastic surgeon and have him examin you and answer your questions.