Call OB or go to ER?

I'm a FTM and I'm currently 38 weeks pregnant and have been having intense pains. It feels like when baby headbutts my cervix, but it's way more intense and kind of coming in 3-5 minute intervals. I also have really bad lower back pain. I do have an OB appointment tomorrow so I don't know if I should wait and just bring this up tomorrow.

Is this just baby getting lower and hitting my cervix? Or is it maybe labor? Also, either way, do you all think I should vall my OB and ask them what to do? Should I head straight to the ER? Or should I just do nothing?