My co-Leader began having sore nipples at 2 mo with her current pregnancy.
One was sorer than the other and kept getting sorer.  She thought at first
it was a plugged duct, but nothing seemed to reduce it.  She's now 7 months
pg.  Yesterday she showed me the "lump".  It was more like a large welt
that went from 5 to 7 on her left breast, below her nipple.  My first
thought was varicose vein, which was confirmed by her doctor later that
day.  Since it isn't a plug and it hurts like crazy to nurse on, she's
going to wean from that side, tho her 3 year old son thinks "weaning is
stupid" (you should hear him discourse on gentian violet).

Anyway, do keep varicose veins in mind, at least in pregnant women.  This
differed from a plug in that it wasn't radial but circumferential.  It felt
to her very much like a lump or thickening, and she couldn't see it well
herself to see that it was more rope-like than blob-like.  When her breast
hung naturally, it looked like you'd expect a varicosity in thick tissue to
look.

Diane Wiessinger, MS, IBCLC, LLLL  Ithaca, NY