I had the same problem, and I still do sometimes. It turns out, even though I thought I was drinking enough fluids, I actualyl wasn't, which can cause contractions. I went to the doctors, and go figure, they were contractions. Now when I feel them coming on I drink some water, and they slowly go away. However, when they start to hurt rather than just annoy you, I would talk to your doctor, because you never really know. That's why we've got doctors right?