Uncomfortable tightness while pregnant

I'm currently 32 weeks pregnant. I've had this uncomfortable tightness in my stomach for the past hour. It's right on the line of painful. I've found a few positions that help, but as soon as I stand up, it comes back again. I've used the bathroom (both #1 & #2), I've been keeping hydrated, and it doesn't come and go. It just feels like my stomach has stretched to its limit and is trying to stretch more. Has anyone else experienced this? Does anyone know what causes it or know any relief for it?