Should I be concerned ?

Question

I'm currently 18 weeks pregnant, when I was around 5 weeks I got lower abdominal/pelvic pains. It wasn't that bad, more like a discomfort, and I was told it was my uterus expanding/growing to accommodate the baby. The main probably stopped around 12 weeks. And now at 18 weeks I feel this pain again. It feels stronger, is primarily on one side (the side the babies on) and is like a piercing feeling. I am not bleeding, it doesn't feel like cramps. Should I be concerned, call my OB or go to Urgent care? Or just let it be.