Contractions?

Earlier this morning I went to bend over and I thought maybe I pulled a muscle in my lower back, on the left side. But the pain was so bad I was in tears, then it started creeping around to my crotch and the front of my stomach where my BH usually are. I sat down to try to catch my breath. It was excruciating. And then the horrendous pain kept coming and going, maybe every 30 seconds. I couldn't do anything but cry and have very short breaths. I couldn't walk, or barley even talk. This lasted for about 45 minutes. Then all of a sudden, I got up to try to see it if would help, and I felt relief. I could breathe and talk again, and the pain subsided. I called a nurse and she said it sounded like I pulled a muscle. BUT if I pulled a muscle, the pain doesn't just go away.... I have no clue what happened. I've been extremely tired since then, and just have had irregular BH for the rest of the day. Baby is moving okay and I have an appointment with my OB tomorrow. Any thoughts?  33w2d btw.