Pulling pain @ 18wks

Brittany • Chloe Elizabeth 7-30-13. Sophia Grace 10-15-15. Baby #3 09-20-16
I'n 18 weeks 5 days, and I have this sharp pulling pain that comes and goes right around my belly button. What is this? I have an 18 week checkup tomorrow but I'm concerned and its too late to call my OB about it.