Could it be?

So, I just went to the bathroom to take a test (seriously turning into a pee on a stick addict) and it was a BFN. When I wiped there was light brown discharge, could it be implantation bleeding or the start of my cycle?  I checked the TWW document and I am technically on day 13 (I ovulated on the 8th). Just wondering if I should NOT get my hopes up.