make up your mind - a baby update

Over the past few months I have been struggling with the question posed by my OB, "Are you sure on your dates?" Well the answer is "NO!" It all started when I began feeling the baby move very early in my pregnancy. I didn't think too much of it at the time because the doc said that I would; this being a second pregnancy. However I wasn't just feeling the flutter-by's, these were full on kicks and punches. And it wasn't just that I felt the baby very soon , I was also measuring big. At my 20 week ultrasound I measured almost 3 weeks ahead of schedule and a month later I was measuring 4 weeks further. My doctor has scheduled another ultrasound to have the baby measured. I'm hoping that it gives us more answers and that I can soon know when this little kiddo is to come be part of our family. I don't think I'd worry too much if I weren't having to plan a C-Section, I'd just wait it out and let him come when  he wants. So now the question for me, the doctor and anyone else who wants to take a wager: Is my due date January 31, January 18, or January 4?