Because I never did and now fell a bit daft for never paying any attention to it! In my defence I was on the pill for a few years so just had withdrawal bleed inbetween packets and never gave it a second thought.
I'm now ttc#2 and periods seem very erratic. But I have no idea if this is normal for me. My period arrived today, so no BFP for us this month, but I'm thinking at least it was a normal (ish) 25 day cycle this time.
So am I on my own for never paying attention to it before?