Several years ago, I also found a painful lump in one of my breasts. Not through self-exam (I am horrible at getting into that necessary habit). I just noticed a general area of pain inside one of my breasts all of the time. It was a couple of months, and I finally went to see my Internal Medicine doctor for my physical.
My doctor then found a lump as she did the breast exam & she ordered x-rays as well as a mammogram to be done. The x-rays were no biggie. A little uncomfortable (strange), but I felt okay. The mammogram was kind of how I had anticipated. Not real easy or fun, but necessary nonetheless. {I believe that they got images of both breasts in the mammogram.} I felt like they were trying to squeeze the air out of me! I made it through, just a little sore afterward...but nothing dramatic.
After the tests, I saw my IM doctor again. My lump was gone! My doctor theorized that I had remarkably produced some milk (a few of years after stopping breastfeeding) which had gotten stuck in a duct. She went on to say that the mammogram probably crushed the lump.
Since then, I have had annual mammograms. Perhaps as a result of my earlier experience?? I've been told by other women (my age and older) that they only have the testing done bi-annually. Someone told me that they do annual mammograms with those who have breast cancer running in the family and those who have a greater risk of developing breast cancer.
Breast pain - MayoClinic.com
Gentle hugs to you ~ try not to worry too much.

Please do let us know how things go, okay?