Rock Hard and Painful

At the end of my shift at work my stomach started to get super hard and ache. So I made myself sit. When I got off and got home my stomach hurt worse. It's a constant ache, along with my lower back. I keep feeling like I have to poop and I'm running a slight fever. I took a short nap but only to be woken up from the pain shooting in my back. Should I call the on call doctor? I'm 27 weeks tomorrow.