Sharp ache in lower left breast when LO feeding - help!

[Kess]

LO is now down to two feeds a day, one first thing in the morning and one before bed, and still has both sides on both of those feeds. Last couple of days my left breast has had a sharp ache in the lower part of it when LO is feeding on that side, which gets more painful as the feed goes on, to the point I stopped him last night and didn't let him nurse on that side this morning. Does anyone have any idea what it is and what to do about it? I got a similar, but much milder (LO has a much stronger suck at his age than my hand-expressing), sensation when I hand-expressed this morning.