How to recognize implantation bleeding

Amanda • Married 6 yrs. Have 1 son. 1 daughter in heaven... She passed from SIDS 5/21/13-6/9/13. Now TTC #3 (our rainbow baby)
We've been TTC for around 6 months. My expected period is the 10th (Tuesday) - yesterday afternoon I noticed a very light (brownish) discharge, and also today. Could this be implantation bleeding? If so, how long does it usually last? And when do you recommend testing? (FYI- my periods always start out heavy (and never brown), so this is what made me think it was not my period).