I know how you feel, I went through this myself just over a year ago. I got myself in more and more of a state as the time got nearer. However, it's worth going through for the peace of mind you get afterwards!
The consultant examined me and asked me to show her what I was feeling - she watched me prodding around and said that you dont find suspicious lumps, they find you! She said I was feeling far too deeply and it was nothing to worry about at all.
But it's good that they send women to breast clinic as a precaution, because I probably would still be worrying now if my GP had just said "nothing to worry about".
Caroline