Week 18 tons of pelvic & groin pressure, normal??

Hi ladies, I'm 34 and expecting my 1st baby. I'm week 18+0days today. I'm petite and gained 10lbs thus far to my present weight of ~130 lbs. I'm mostly inactive and have a desk job. The pain and pressure started around week 16. I would get it only when I stood up or get out of bed. It's this intense pressure pushing outward that makes me freeze in my tracks and makes walking very hard. It feels like everything is about to fall out. Sometimes I feel something pulling in, but I can't distinguish the sensations since it's so intense. My cervix is getting pressure as well as my vulva area. I've contacted my OB office and they told me to rest up since those are the only symptoms I'm experiencing (no discharge, etc). Sitting is the only way to relieve the pressure/pain. I see my OB at 20 weeks for checkup and debating if I should go sooner. Are any of you experiencing something similar or is this a common 2nd trimester symptom??? Thanks for the feedback!