Contractions - Labor or Not?

I have been having contractions since this morning. Initially, they were pretty irregular in terms of timing, but now they are a few minutes apart. I wouldn't say they are painless, but they are not so excruciating that I can't keep doing whatever I was doing through them. I have been taking it easy and lying in bed, but I'm not sure that helps that much. So technically, now, I should call the doctor's office and they will tell me to go to the hospital, but I'm reluctant to go unless I'm sure I'm in labor. My concern is that since I'm past 39 weeks (the magic number from an insurance perspective for a doctor not to get sued for doing an elective c-section), if I go to the hospital, the doctor will deliver the baby regardless if I am in labor or not.

So how do you know if you are in labor? The baby seems a little lower, but not too much. Contractions are 4-5 minutes apart but don't last for more than 20 seconds. Contractions are localized to the lower abdomen and back. I have a history of having contractions close together without going into labor. I have not lost my mucous plug as far as I can tell and I'm not having any unusual discharge (bloody show or the like). I just finished eating, so it would be at least another 5 hours before I could have surgery. We are going to wait it out a bit before doing anything. I like the doctor who is on call this weekend, but I would be catching her at the end of over a 48 hour on-call shift where she has been covering for 4 practices, so who knows how much sleep she has gotten the last 2 days and I'd prefer to have surgery done by a doctor who may be fresher.