Labor?

Michelle • 21 year old FTM due January 2016 ❤️
Hi all! 
I am 40+6 and a FTM. I started feeling very gassy today, and am having lower back pain accompanied by very strong tightening in my belly. Uncomfortable and painful but nothing awful. The thing is, I've heard contractions are more like period cramps but this just feels like uncomfortable pains almost like constipation but with back pain, I'm confused if it's labor or not? I've been losing parts of my mucus plug all day. Should I start timing? 
Thanks all!