What is it

I woke up this morning with what felt like back ache that i get when im due AF. It disappeared and then came back on and off. I walked 30 seconds to my granmas without a coat, its not really cold to be honest here in UK. Spent 10 mins and walked back home. I sat down and all of a sudden my lower back started pulsing but aching and i couldn't catch my breath or move. It disappeared and i was left with back ache again. Then it got worse and settled off and then came back really bad. It doesnt feel like nerve pain. Ive taken paracetamol and normally paracetamol doesnt do anything for me but i needed something. The pain keeps coming and going. My partner paniced thinking it was labour, im only 26w+5. Any ideas on what it might be