Its hormones for me too, can't be bothered and my orgasm has left the building.
Coupled with the knowledge that it is still a bit sore arouind my epis site when we do it and the fact I go to bed at 8.30 and DD not napping at all during the day, its just not happening.
DH is good though, he isn't hassling me at all.
Nice to know libido comes back when your period does though, I didn't know that.