Bec, it is common to have some small amount of spotting after transfer. your cervix is irritated when they're trying to get it lined up and insert the catheter, so it can "bruise" a little - hence a small amount of spotting. you CAN get implantation bleeding, but it's not really common, and i would guess it is too soon after transfer for this to be the case for you - implantation normally occurs somewhere around day 8 of embryo develoment (give or take a day or two) - i'm assuming your embie would be a day three at transfer, so still too early for that one... i doubt it was an embie leaving you yesterday - they're so tiny as to be invisible to the naked eye on transfer - and wouldn't have developed into a large enough mass to be visible overnight

hoping you get your BFP very soon

BG