Hard immovable lump in breast. Scared to death

I'm 35, mum of two young boys and I've found a hard lump in my right breast. I cannot move it at all. It's rather deep down and feels like a marble. 

 

I have a telephone consultation with my GP on Monday and I am scared to death!  I don't know what to do.  Just wanted a place to vent and maybe speak to others who may have some advice.

 

I am shaking and crying. I can't look at my boys without crying. I don't know what to do. I can't leave them!  I just want to wake up and realise this is a dream.

 

I know it may not be what I fear but the fact that it's so deep down and cannot be moved makes me fear the worst. I don't know what to do x