Cramps/Contractions?

🦋 Mother and Queen 🦋

So I'm 33 weeks and 5 days along. Earlier in Walmart when I was walking I had a bad wave of dull pain in my back and it had me holding my breath for about 30 seconds. I was slouching over the shopping cart. I seen a video on YouTube said Braxton Hicks don't reside in the back area. When should I worry and what should I look out for in terms of real labor?

Thanks for all replies 😊❤️