How soon can morning sickness begin?

I have a few more days until I can take an early test, but tonight I have begun to notice a sudden wave of nausea (no vomiting) and have been having what feels like dull menstral cramps. Hubby and I have been TTC for a couple of months with no luck, so I'm trying not to get my hopes up. One can't help but wonder, though. Theoretically, I am 7 DPO (I've been using CM and BBT to base, not OT). Just curious to receive input from other mothers/expecting mothers on when you typically see MS rear its ugly, yet also beautiful head.