back and abdominal pain - something serious?

I'm 18 weeks pregnant and have been having what I thought was round ligament pain for about a week, located mostly on the right side. However, this is now being accompanied by pain in my right lower back that feels kind of like a pinched nerve. The abdomen pain kind of comes and goes but is usually there at least a little bit. Could this be something serious? Or can I just wait it out and call the doctor if it gets worse?