This happened to me too!
I was 33 weeks with my son and I had an episode of contractions that lasted on and off (most mostly on) nearly all day. They were just as you described - quite painful and radiating down into my legs, back etc and I couldn't get them to stop.
I was home alone with my DD which was the only thing that stopped me going to the hospital, I'd already had one baby and they were starting to feel like the real deal to me.
Thankfully they did stop on their own and it didn't happen again - DS was induced at 38 weeks.
A few days later I had my OB appointment and he checked me and I was still closed and long so he put it down to BH - but I got a severe telling off for not going to the hospital.