I had this last night too. I'm 38+5. The back pain seems to have dyed Down abit now tho. I hope it's early labour
Some women can have contractions and no pain just the tightness in the stomach. Try and take a warm bath to see if it increase or goes away. And drink some water.
im a first time mom, but from the way other mommys on here describe labor it sounds like it could be the start of it, i'd call your hospital and see what they say to do or go in.. good luck