Back contractions

Lily • ERN 9/4/19 🖤🧡

Can someone explain how back contractions feel? I’m a FTM and my back will randomly start to hurt then my stomach will get tight. I don’t have period cramps just my back cramping up. I am scared they are contractions rather than Braxton Hicks but I’m not sure. I am 36+2 and on Nifedipine to stop contractions due to preterm labor at 33 weeks.