Contractions? Braxton Hicks?

I'm currently 39 weeks pregnant and for the past 2 days now I've got this constant tightening in my belly it's only the lower half but it stops for a bit and comes again. Plus ive had constant brutal back pain. I cant tell if its contractions or braxton hicks but I dont wanna go to labor and delivery to be sent home (it's a 30 minute drive.)