Light brown spotting

Kim • Pregnant with #1 after about a year of trying. Due end of October and very excited!
I'm 6w4d pregnant with my first.  I've had all the typical symptoms of pregnancy and everything has been fine so far. But today I started very light spotting. It's light brown.  I just noticed it about 20 minutes ago.  
I've missed one period already, but if I weren't pregnant, today would have been when I start my period. Help!  Should I be worried?