Cervix Pressure, FTM

Posting here because I didn't get a response in my other group. I've had a little bit of pressure come and go in the last week. I'm 18 weeks 3 days and can feel my son moving around so I feel like he's alright but I'm paranoid to go into labor extremely early and lose him. This is my first baby, I lost my last pregnancy early on so I've never made it this far. I'm not sure what's normal. It doesn't hurt, it just feels like a cramp or ache every so often, like something is pushing on it and I can tell it's my cervix. Could it just be from him sitting low? I haven't had an ultrasound since 7 weeks so I haven't had my cervix checked to make sure it's how it should be, but I also haven't had any bleeding. Is it normal or should I be calling my doctor?