Cramps

This is my 3rd day straight of getting postive tests. ? My period was supposed to start today. Every so often I'll get a cramp that feels like a moderate menstrual cramp, but it only lasts for 30 seconds at the most and then I won't get another one for another several hours. Anyone else experiencing this?? I'm hoping it's just my uterus expanding to get ready for baby! That's what I've read on Google anyway...