Pregnancy and predicted period

I've always been super regular with my periods, every 28 days on the dot. And I've always used a period tracker because of the convenance. Now that I'm pregnant, I've noticed that I can always tell when my scheduled period is due(if I wasn't pregnant) by how emotional and moody I get, I usually check the tracker to confirm that's the reason. I find it very odd and fascinating that I'm not super emotional all the time, just when my period is due. Do any other expecting mommys out there experience this?