Well, this is a very vague symptom; you could have a slight infection developing, it could be a hormonal issue (your breasts tend to swell if you're pregnant or just before your period), you could have some swollen lymph nodes somewhere that are producing general swelling... The general rule of thumb is, if you're a younger woman (before menopause), and you notice a breast change, wait a month (through the course of one menstrual cycle). If the change remains, see a doctor to find out what's causing it. Also - if this swelling increases or becomes accompanied by pain, redness, heat, or other signs of infection, then see a doctor ASAP, OK? Because this change would signal something developing quickly that should be loked at. Good luck - I hope this swelling disappears on its own soon. PJH