Hi,
my RE told me i could expect some cramping and spotting days after the transfer. So that might be what that is or it could be implantation since ur embies are 5 day and not three day like mine. i never had the implantaion spotting i only spotted a few drops of red and then some brown discharge on the day i was supposed to get af. So good luck!! i hope it is implantion bleeding and u get ur BFP!