Period feeling?

I'm 41 weeks and all day have been having this feeling like I'm going to start my period. It's not pain but it just feels like constant pressure in the lower stomach that never goes away. (I've been feeling it since I woke up so about 15 hours now). When I first used the bathroom I did see a big mucus looking blood in the toilet and had some on the toilet paper but that only happened once and I had spotting for a couple hours now it's all done. What does this mean? Yesterday I got checked and was only 1cm but according to the nst had consistent contractions every 2-3 min that I had no idea was happening.