Kristen, are you about to get your period? It's not unusual to experience sometimes painful swelling in or around your breasts as part of your menstrual cycle. If you don't think that's the cause, you may have a low-grade infection somewhere that's settling in your underarm lymph nodes, and causing some general swelling. Or, you may have an actual breast infection. The least likely cause of this could be a rare form of breast cancer, inflammatory breast cancer; but it's highly unlikely, so please don't stress over that.

I'd suggest you keep an eye on this; if it doesn't disappear within a few weeks (or certainly if it gets worse: more swollen, red, hot, itchy, more painful), then you'd want to see a doctor to find out what's up. Take care- PJH