38w1d with lower back pain

Before calling my on call doctor just want you ladies advice. I've been having really bad lower back pain for about 3 days now. Tonight it's been bad to the point it kinda hurts to walk. I feel a little tightness in my stomach but not any pain that's unbareable. At times it feels like I'm coming on my period but of course that not the case since I'm pregnant. Not sure if it's a start or labor. Last I was checked I was 1 1/2 dilated and 30% effaced and he said he can feel her head. Should I call or try to relax? Thanks 😘