I normally get my period every month before my sister does. However, this month she started her period before me. She started 12/6. Last month, I don't remember if my husband and I even had sex. I have been busy working and so has he. That everything just slipped by me. At first, I had some cramping. Right after my period - and the start of my ovulation, I had some slight spotting - but now I haven't had anything but some cramping, and nothing! I have tender breasts, but I usually get those during my menstrual or before I am starting. No sign of it. Is it possible for our menstrauls to change - and my sister end up with hers before I do?