Labor in your back?????

Dominece • Married with three lovely kids 2 boys and a lil princess and another princess on the way 3/3/15
How does that actually feel? I've been having an on and off type pain like someone squeezing but only in my back. I have a doc appt tomorrow but I'm 31 weeks so not sure what is a serious scare or something else. I also took a relaxing bath to try to help and as soon as I got out more came. Thanks in advance for the help ladies