Contractions.

A question for the ones who have gone into labor before... What does the beginning labor contractions feel like? This will be my 2nd child but I never went into labor with my 1st pregnancy. I'm 33W3D, I lost a bit of my mucus plug today & almost immediately started contracting a bit. It starts out as light lower back cramps that slowlyish works it's way around both my sides & into my pelvis all while my stomach tightens.