No matter what time it is, when in doubt, call your doc. That's what he/she is there for, and what they get paid for. They are used to being on-call at all times, especially OB's since you can't always plan when the baby comes.
I think I went to the hospital because of horrible pelvic pain 2 or 3 times during my pregnancy, that ended up just being the cartilage in my pelvis stretching, it certainly wasn't labor since my daughter didn't want to come out even at full term. I felt a little silly afterwards for making something out of nothing, but I felt so much better knowing they'd checked the baby and me out and everything was ok.