it can come out and you may not have even noticed or maybe it just hasn't come out yet.

Some never come out

mine came out when my doctor had to pop my water. So a few hours before birth

with my son I don't think mines came out at all

mine didnt come out until about 2 or 3 days before i turned 39 weeks

I was told in my labor & delivery class that not everyone's will come out at the first sign of labor. Sometimes you get the strong contractions first and the mucus plug will come afterwards. Hang in there!