J.P.
There was probably stress and her eating habits may have changed a bit, plus yours changed. I have never heard of a duct developing from carrying a baby, and definitely not from an Ergo, or I would have a constant plugged duct! Love that thing. I'm also wondering if all her screaming could have made you have a let down, but it wasn't time for her to eat? Just throwing things out there. Just make sure that she feeds for awhile with her chin pointing at the plug until it is totally gone for sure.