Tightening/stomach cramping and lower back pain... Braxton hicks? Idr what they feel like because they always happened when I was sleeping in my last pregnancy.
It could just be braxton hicks. It's hard for me to say because that's actually how it felt for me at 32 weeks with my first when I was going into preterm labor. Can you track them? I would try that and if they're close and consistent I would go to labor and delivery to be safe.