Is it normal at 3 weeks post op for one breast to be more swollen than the other?

Thanks for your inquiry, but without pictures and more details it is hard to advise.  Some asymmetry can be normal, but other cases many represent a problem--please call your surgeon to discuss.  

After breast augmentation, your breasts can heal at different speeds. One may settle sooner than the other. One may resolve swelling more quickly. One may soften before the other one days. At 3 weeks, you’re very early in the healing process. Unless the swelling is new, one breast may just be healing a bit slower than the other one. If the swelling is new or significant, you may want to check with your plastic surgeon to ensure that everything is OK and your breasts are healing well.

Thank you for your question.  It is quite common for one breast to be a bit more swollen than the other following breast augmentation surgery.  That being said, increased swelling, redness or pain should be evaluated.  Best to follow-up with your plastic surgeon.  Good luck.