Preterm Labor at 20 Weeks?

I am cramping terribly bad. It hurts all over and I feel super nauseous. I have been up all night with it and it just isn’t going away. I called my obgyn to ask them what they think I should do. The nurse I talked to goes “could be preterm labor but let me talk to Dr. Dowell and see what she wants done.” Then hung up as I’m sitting there like Umm what.... do I go to the ER or wait for a phone call back or what?!