Hi there - I'm certainly not an expert charter like many of the other gals, but I would suggest a 'less is more' approach. Perhaps you are BD-ing too often, maybe try every other day beginning @ day 8 until the AM of your temperature rise might help. Good luck!
I'm sorry for your BFN and hope you get some helpful answers from the RE. This is just in response to the previous comment -- there have actually been some recent studies to show that daily sex (or at least daily ejaculation) is best for sperm health: news.bbc.co.uk/.../8125934.stm