My GP told me yesterday that 3-5 days is ideal because losing blood is losing iron. I am on drugs to make mine only last 3 days now since mine have been averaging 8 days to 3 weeks!

I think your last cycle was like my last one - there was probably something wrong with the corpus lutenum so it couldnt keep producing progesterone, hence the temp nose dive and AF during the LP. If you have concieved before I wouldnt think there would be anything wrong with your lining