Officially Starting the Third Trimester

Yes, it's official. I am getting large.
Someone at work the other day (a customer) said to me, "Wow, you must be expecting a Christmas present baby." I replied, "Uh...try Valentines Day." Someone else said (Oh wait, like 10 people) ,"When are you do?"
"February."
"You're HUGE!."
My mom reassures me that I don't look like I am nearing full term, and I trust her opinion more than some old guy. I have decided that I am in the third trimester. It is never quite clear how to calculate where I am in gestation, there are 40 weeks in pregnancy, and that somehow equals nine months which somehow also equals three trimesters. How does that work? Am I six months pregnant? Seven? In the seventh? I'm 27 weeks, so if each trimester is 13 1/2 weeks, then I am entering the third on Tuesday, or so. No, last Thursday. I've been paying so much attention to the passing of each week that I really don't know how to comprehend the idea of having the baby early, which apparently is normal to be up to 3 weeks early (37 weeks), or worse, to have the baby late, which is also normal (up to 42 weeks). What??? My due date could actually be January 28th or March 3. My sister Amy is due January 28th! What if she's late and I am early! Oh, the zany nature of procreation. I can hardly stand it. What's the point of even trying to keep track. It's apparent, anyhow, that I am bigger today than I was yesterday so I AM moving forward in time.