advice appreciated please :)

Just a little confused at the moment. My boobs have been tender the last couple of days, and are a lot more tender today then they have been.  I'm also having spotting which appears to be brownish. I'm due this Sunday (18th) tested this morning with fmu with a BFN. Just wondering if this has happened to anyone else and ended up with a positive? Don't know wether to just expect my period or my rainbow is trying to let itself be known without the positive!