I'm sorry it's taken so long to get back!
When Thomas was 3-4 months old, I noticed a lump far back and up on my left breast. It was tender, but not painful (if that makes sense). I treated myself for a clogged duct, but it didn't go away, so I went to my internist, who prescribed antibiotics on the assumption I had or was getting an infection in my breast or respiratory tract (which is typical for me). After several rounds of antibiotics, he referred me to a breast surgeon, who did an ultrasound and said my lymph nodes were enlarged, but said it was due to breastfeeding (I never quite understood why my lymph nodes were affected by nursing, but that was his belief, and that of another surgeon I ended up seeing several months later).
It did become painful eventually. When I saw my OB/GYN in January (Thomas weaned himself in December) I asked him to order a bilateral mammogram and ultrasound (it was due anyway as I have a history of fibrocystic changes and had had two biopsies before that point). The mammogram and ultrasound showed solid growths that were deemed "suspicious" by the radiology rating scale, and after consulting with my oncologist (I had colon cancer in 1999), I was referred to another surgeon, who ordered a biopsy. This was in March 2009.
I've had two fine-needle aspirations, and then the one (looking for the name of it) in March, which was different. They are not painful, and the only thing I was supposed to do was to keep ice on my breast for a little while after the ultrasound (they do ultrasound to guide the needle into the right spot). I didn't have any soreness at all and in fact went to Target as soon as I left the hospital.
ETA: The March biopsy was a vacuum-assisted core biopsy.
If you have any questions (I've had to write this in bits and pieces, so it may not make a lot of sense, or may not answer the questions you have), please don't hesitate to ask!