Achy back!

I’m 39w4d and I am not showing any signs of progression really. Last Friday, the 6th, I got checked and my cervix was closed. I have had a few very very mild contractions that my NST’s have picked up, but nothing that I can even feel. However, my lower back has been super achy since Thursday afternoon. I know baby is head down, face down because I had an ultrasound yesterday so I don’t think it’s his position. Do you think this could be back labor or just another “end of pregnancy” symptom?