Anxious about result lump in breast

I am at the Brest clinic tomorrow afternoon. I'm really scared now and the last week has been one of the longest weeks ever !!

I am very positve person but this last week has tested my positve outlook.  I initially went to the GP with breast and underarm pain and pain in shoulder. She found pea sized lump in my left breast and referred me last week.

I understand that BC usually presents no pain but I  curious why I'm in constant pain especially my shoulder  blade and underarm. Has anyone else had pain with a lump ? 
thanks D