Incompetent cervix?

JTJKH
This is my 3rd baby. I'm 20 weeks along since I was about 15 weeks i have felt thin down there that's the only way I know how to describe it. The past 3 days it's almost like I can feel the baby crowning. If you've had kids before you'll know what area I mean that I'm talking about it feels like the baby is going to fall out of me. There's this dull pressure there. It's so weird I don't know how else to describe it. I can feel every move the baby makes in my vagina not my stomach like I've felt with other pregnancies... Has anyone else experienced this? 
I had an ultrasound at 15 weeks to see if the placenta was okay and everything was. I'm so confused why I feel like this way down there. I feel like I could put my fingers in my vagina and feel the baby that's how close I feel to feeling thin with the dull pressure and kinda shooting pain but not really painful if any of this makes sense