How long does the swelling in the incision site last?

Thank you for sharing your question. Unfortunately without pictures it is difficult to offer definite advice as you may be experiencing normal healing with scar maturation that takes months or you may have a suture related reaction that needs to be seen by your surgeon.  If you are seeing little improvement discuss this with your surgeon, they are your best source of advice. 

here is a predictable pattern to the swelling after surgery.  The swelling increases for the first 3 days and then begins to decrease.  The swelling in the incision has mostly improved in the first 3 months, but takes a year to see the final result.  I usually recommend massage of the incision beginning 3 weeks after surgery.

Swelling after breast surgery is normal and can persist for weeks to months after the procedure.  Most of the swelling will resolve in 6 to 8 weeks, with some persisting for up to 6 months.  Nonetheless, to ensure healing is progressing normally, I would recommend you follow up closely with your plastic surgeon. Best wishes.