Hi, it sounds like you need to get yourself back to the doctors for further tests.  The good news is, cancerous lumps aren't usually painful, so the fact that it is sore could be a good sign that it is something else.  

I found a small hard lump in my breast on Saturday, went to the doctors yesterday and am now waiting for an appointment at the brest clinic.  I'm pretty scared.  The doctor mentioned 'cancer pathways' and when I rang to make the appointment they said I had been highlighted as an urgent case.  Just waiting for the clinic to ring with an appointment date.  I keep swinging between perfectly calm and reasonable, to convinced its cancer and imagining how I'll tell my kids.  

Try to be brave and go see the doctor again.  It's the only thing you can really do to put your mind at rest.  

Good luck

K