hard round lump under skin on my left nipple

Katie
I'm 15 and have just discovered a pea sized, hard round lump under the skin of my left nipple. 
It's a little uncomfortable to touch, and my nipple is quite itchy. 
When I try and move it a little, it feels as if it's attached to something, like it doesn't move with my finger. 
My first reaction was to cry.. I know that sounds pathetic but this has been a worry since I started puberty, having cancer. 
I don't know what/if there are any side effects to having first signs of breast cancer, but I have been feeling weak, tired and unmotivated the past few weeks.
My bampi, mum and Auntie have had some sort of cancer. That's what worries me.
Please help me!