I Am 36 Trying To Get Pregnant Fro The First

I am 36 trying to get pregnant fro the first time. I have been feeling pulsing and tightening in my uterus last week and once the week before (which has never happened before), and today my period started. I just want to kow what's happening, I was told its likely not an early miscarraige, but how come my body has been acting different from previously?