Girls, hi. I have pain in my stomach and down there, my belly is press…

Girls, hi. I have pain in my stomach and down there, my belly is pressing and at the bottom it feels like an opening. I'm feeling like I'm giving birth but not me doing that on my own. This has never happened before. I still have three months until full term. I don't know what will happen, how I'll endure it. The gynecologist says nothing, everything is normal on the ultrasound. Has anyone had this?