WTF?

I woke up this morning with cramping and spotting. It is CD 12. Everything I read says mid-cycle spotting can be normal but this hasn't happened in more that 3 years of charting. My temps have been erratic, but that does happen sone months pre-ovulation. It was a rather heavy spotting day, with cramps and back aches and now a headache. If I didn't know better, I'd think I was about to get my period. But that can't happen on CD12 right?
I just hope, whatever this strange day is all about, it doesn't screw up my IVF cycle. I'm supposed to start estrace in 5 days.