J.S.
I had that happen with my now 4yr old, and I think it was about 2wks after I *thought* I was done producing milk. For me, hot washcloths felt best. I just soaked the washcloth in hot water, rung it out a little and laid it on my breast. Or, I would go in the shower & put the water as hot as I could tolerate & let it stream on my breasts--that helped a lot too. Sometimes it seems that stopping nursing can be as painful as starting out!
Good luck & hope this helps!!