:grouphug Geek. You are absolutely doing the right thing in getting it checked out. It probably is nothing, but young women do get breast cancer and a doctor should NEVER blow you off when you come to them with a lump.
I feel for you. I'm still (relatively) young but all the women on my mom's side of the family have had breast cancer - I feel like a ticking time bomb. :ohno
Keep us updated.