Uterine tightening at 14 weeks

Hi ladies, I'm pretty sure this is normal, but just wanted some reassurance... is it normal to get uterine tightenings (basically BH) this early? They already started at 13 weeks. Not painful, just uncomfortable. With my first pregnancy they started at around week 20 so I know that the feeling is normal... just a bit uneasy that they started this early.