This may sound silly....... but mets?

Ok, I am a newbie, when it comes to all of this cancer stuff. I have truely educated myself so I thought. I know my diagnosis, I get my treatment plan, but I dont understand mets (brain, liver etc) and what kind of stuff do you look for when you cant feel a lump in those areas?

I dont think I was "sick" when I got diagnosed, could have been when I got the "flu" last year it could have been a sign... but other then the lump sticking out of my boob... even then the doctors didnt think anything. How will I know if I have any other tumors (ok, had a pet scan and nothing was shown, although that only shows tumors at least 2cm.) are there signs, how do I know my "chemo brain" isnt really something else.
Truely, I am not trying to be paranoid, if it happens again, I will deal with it at the time, but I dont want to get at it too late.

Can any of you recommend a site that talks about these mets things I see on the site?