I had the same thing happen to me some years ago. I was at the doctor's the next day. (Both my grandmother's died from breast cancer, and one had found it from a lump in her armpit.) It was an infected lymph node. My doctor told me it came from shaving everyday and the applying deodorant right away. It just blocked things up. I was on antibiotics for about 10 days and couldn't shave for awhile. I now shave every other day at the most. So go to your doctor and get checked out. It will most likely be nothing, but it is best to know what it is and how to deal with it.