Long time lurker, first time poster and this is going to be looooong! 
First a bit of background - Have been TTC for 16 months had BFP in January after spotting and MASSIVE temp drop which then shot back up. Saw heartbeat at 7 weeks (scan at EPU due to continued spotting) but then lost the baby at 8 weeks.
Have been trying ever since and had no luck. As it took a while (10 months) to get my first BFP I did expect that and we have been to the doctors who has started the fertility clinic referral ball rolling.
I am supposed to be going for my blood tests tomorrow and AF was supposed to be here yesterday, have had a regular 28 day cycle for quite a few months now. I have spotting EVERY single month and this month was no different. Started on 9dpo (I temp so am pretty certain on ov date) so I knew that she was on her way. Massive temp drop on Tuesday and have been cramping since Saturday however, she hasn't shown her ugly mug. Done a test this morning just so I could stop googling "temp drop and spotting but still BFP" and having any hope and it was, of course, BFN. Temp drop a little more today but still above the coverline, but I don't think the coverline means anything anyway really does it?
I am just so confused as to what is going on. The one month when I want my AF to come so that I can get these blood tests and get my referral and she has gone AWOL. I am still spotting but it's just not ramping up. I normally get the temp drop on the day of AF, my temp seems to stay up right until the bitter end despite the spotting.
Could it be that I am so wound up that my AF is late? Is it not usually ovulation that is delayed by stress rather than AF? 
Has anyone ever had this or can shed any light on it?
Thank you and congratulations if you have made it this far, I would really appreciate it if anyone could help me out with some theories.