Unusual breast lump

Hello, 

A long time ago in the shower I felt a piece of ropey tissue in the lower part of my right breast it felt like a lumpy vein and I could see it through the skin. It disappeared when I got out of the shower. 
On Christmas Eve I felt the same thing. This time it has not gone away. It is sometimes more or less pronounced but doesn't go completely. 
It is shaped like a letter C and feels like a bumpy worm under the skin. It moves about a bit and I can grab it with my fingers. 
I went to the GP and she says it doesn't feel sinister but has referred me. 
I have an appointment on Thursday and am going out of my mind with worry. I am 44, have 2 young children and I am terrified that I'm not going to see them grow up. 
Is there anyone who has had a similar experience? 
Thank you, 

Sara x