Back labour?

I’m not sure if anyone has gone through this - I’m 40 weeks today, had my cervix checked and was only 1cm dilated and not fully effaced. My cervix was long but soft and I’ve been having the normal bleeding/cramping since. Before going, I started having really bad lower back pain but was constant and got worse when I walked. Now, I can’t walk without gripping the wall and my legs (really my whole body) shakes as it hurts so bad. Is this back labour? Or did I tear something? My OB seemed unphased when I was in her office and mentioned the onset of the pain this AM.

TIA.