Sore swollen boobs

I've never suffered from PMS, lucky really, just about half a day beforehand when I get a bit weepy.

But the last couple of months, I've had really swollen, sore boobs for nearly a week before my TOM - normally it has only happened on that day before.

Does anyone know what causes this and if there's anything I can do about it?

I've read from other threads that LC can cause breakthrough bleeding, but generally seemed to lessen PM symptoms.

I don't get any other PM symptoms still so maybe I shouldn't be whingeing, but if anyone's got any answers or solutions I'd be grateful.
Thanks, Jay