I am experiencing a similar thing right now. Last week I noticed a knot or lump just under and in the center of my breasts. I was getting ready for bed and took notice but thought "I guess I've never noticed that bone before..." The next morning, however, as I was getting dressed, I noticed it again. I felt around and it felt a little tender, and during the next few days it seemed as though my bra really seemed to cause discomfort (probably nothing more than purely mental) Anyway, went to the Dr. today, and she says she's pretty sure it's just my sternum. Not sure why all of a sudden it protrudes, but..... go back in a couple of weeks for a follow up. I have been dieting, and asked if any way possible it could be related to that. I was told it could possibly be related to that. Any suggestions or input would be greatly appreciated.