Large breast lump, clear ultrasound?

Hi, I am 21 years old and about 2 weeks ago while preparing for a bath I discovered an painless oval, movable, rubbery lump in my upper right breast about the diameter of a ping pong ball.  I went the next morning to my physician, who evaluated it and seemed concerned, and made me an appointment for a mammo and ultrasound at the local hospital, and also with a general surgeon on the 16th of this month. They did not give me a mammo, because they said I was too young. Even though the technician could feel the lump when she went over it with the ultrasound device, they claimed they could not find anything abnormal and that my breast was fine. I left more unsettled and with more questions, because this lump is well defined.  2 weeks later, the lump is still here, and my appointment for the surgeon is this Friday, but I am afraid. The lump is not hard to find at all, and it is easy to feel that it is there, given the size, and it is clearly there as all of the doctors I've seen have felt it themselves.I am afraid it will be written off as nothing and I will have to live oblivious to what this could possibly be. But what could it be? How could it not show up on the ultrasound? What will my surgeon do, more tests? A biopsy? I'm terrified. Any input would be helpful.

[Cleveland Clinic]

Dear kizmetstar13:  Lumps can be many things but it is impossible to speculate without evaluation.  Ultrasound is best at differentiating between a solid and fluid filled structure.  So if nothing showed up on ultrasound, it may not be the right test for this lump.  The general rule of thumb with a new palpable lump is that it requires evaluation.  If the surgeon is concerned, he could do either different imaging, a needle biopsy or remove the lump depending on what he feels.  Breast cancer at 21 is quite rare.

[kizmetstar13]

Also, if it helps, I had a yearly routine breast exam at the health department in Jan, nothing abnormal, and the lump is located in my right breast in the upper portion above the nipple.