Don't worry. Do something. I don't think that it is anything abnormal, but breast cancer does spike a bit while a woman breastfeeds. I say get it checked out and have some peace of mind.
Mind you, I have typing this from a hospital room where my husband is recovering from surgery from colon cancer. He waited a month before he checked on his problem. He knew it could be caused by so lmany things. He didn't see a doctor until he knew in his heart what the results would be. Caught a little earlier and he wouldn't have had to go throught major surgery.
PS. He has a clean bill of health now.