My clinic always said to take progesterone up till BT. If neg stop and if positive continue till 12 weeks. Was it a fresh or frozen embryo? My clinic worries more about progesterone levels in a frozen cycle as in a fresh cycle you should have a corpus Luteal cyst to help with progesterone levels if the cycle is successful.. Does that make sense?
I also had lots of spotting like you are talking about during my TWW with my last embryo transfer and it still stuck. I know it's easier said than done but if it's just 'spotting' and not enough to soak a pad it's usually harmless from what my FS told me. Good Luck Xx