early labor symptoms?

I'm 36 weeks & 4 days , I've been having on and off cramp since last Thursday but today I woke up and the pain is a little more consistent and hurts a little bit more I'm not really sure if they're contractions or just gas pains I feel as if I'm constipated and have to poop but every time I go to the restroom nothing comes out and I know I'm not constipated cause I've already used the restroom twice today. It's also accompanied by back pain , I could still move around and walk and stuff but it's starting to get more uncomfortable and to the point where I have to kind of breathe through the pain and stop what I'm doing. Could this be early labor? Should I call l&d? I'm scared to just go in as I was just there last week and only progressed to 2 cm and they sent me home :-(