[sfem]

Interesting question. Probably as many answers as people.

For myself, there are a few kinds of discomfort.
Itching. This happens mostly around or in the nipple. I read something somewhere that as they expand, the skin thins some and this causes it to dry. I don't know about that, but I do get itchy there from time to time. I can't say if it is growth or not, but I can say that Vaseline Intensive Care lotion fixes it right up.
Bump them and they hurt. Yeah. Not certain what causes it, but massage helps to reduce the sensitivity, and reduces the throbbing after bumping them for the 87th time so far this morning.
Slow deep ache. I think this one is the surest sign of real growth although I have no real proof this is so. It just feels like that to me. Nothing helps with this one. It is well below the surface, but not in the pecs. They just ache. Sometimes for hours or days at a time. Not a horrible pain, just an awareness of what feels almost like pressure below the surface. It doesn't happen very often, maybe only once a month or so although that could be off. I don't track it.
Then there is the agony of finding a gorgeous bra or top and not being able to fill it properly.