I don't remember how long ago I started noticing this sensation, but it used to occur once or twice a day and is now more like 5-8.
I'll feel a cramp or a tightening at the bottom of my uterus. Sometimes it feels quite firm to the touch, sometimes all the way up my belly. It lasts for a matter of seconds and then fades.
I'll assume this is normal uterine growth/stretching but am curious if others feel something similar. Other thoughts are that it's the baby pressing or Braxton Hicks, but it doesn't really match the descriptions I've read.