Sore lower belly

I’m 18 weeks and began having a sore belly anytime I sit for a while. And especially when I first stand back up, it aches a bit and is hard to stand up totally straight right away. It’s all the way on the lowest part of my baby bump, honestly probably below where baby sits down low.

Is this normal? Does anyone else have this? I have an appointment this week so I’m going to bring it up. But my thought is maybe it’s just because of the weight of the baby and the fluid? I dunno.