I would say your body isn't regulated yet, Bearsmama.
I also got my first PPAF this time at when ds was about 9.5 months and each of the periods I have had since have come at 36 days, 38 days and 35 days. When I'm not nursing, I'm exactly every 28 days. Like total clockwork. Always.
If the only time you had unprotected sex this cycle was a month ago, then I think it would be virtually impossible to be testing negative at this point. At most, sperm can live for up to 5 days inside a woman's body. So even if you ovulated 5 days AFTER you and dh did the deed and a conception took place, you would be at least 19-20dpo by now and would have enough hcg to show on any hpt.
But, if it makes you feel any better, I'm sitting here on cd31 hoping that af finds her way to me this month.
Actually, I'm praying...lol.
~lisa~mama to 3 boys (1/02, 5/04, 12/06)