How to time contractions

For the past couple of days I have had really bad back pain that radiates to my tummy. It only hurts in my back and my tummy gets rock hard but when they are in my back its last a really long time and I just have spurts of intense pain. I guess my question is how do you time because to me it's pretty constant for a couple hours. I'm a FTM and I'm 38 weeks 5 days at my last appointment I was dilated 1 and 50% I have been walking ALOT from work and then last minute shopping so idk if that has something to do with it or not.