Braxton Hicks or Contractions?

I am 31 weeks pregnant.For the past couple of days I've been having tightening in my lower abdomen.My stomach gets hard for couple of seconds and comes back every 5-10mins.Its quite painful.And I have sharp pain on my lower left side on my abdomen.This is my third pregnancy and I've never experienced anything like this before.Im drinking so much water and peeing so much😣After these tightening feeling goes away I get the urge to pee(TMI) sorry.My back hurts afterwards.Are these contractions or just Braxton Hicks ? It's so hard to stand up straight when I'm having these tightening feeling but it does go away after a couple of seconds and keeps coming back.