Braxton Hicks

At the Dr's yesterday she asked me if I've had any Braxton Hicks contractions.  My response was "no", but when I got home I wondered if I had.  I'm 23 weeks with my first, and I read that Braxton Hicks are common to start this early.  I have no clue if I've had or not. I feel like with your first all these feelings are foreign, and who knows what it feels like!?!  Can someone please try to explain the sensation?  :)