All I have to say is that if the show spans 2 years from the day Rick woke up and there's any chance that Shane was the father of Lori's baby then she has had the world's longest pregnancy. Rick was only in a coma for about a month and it only took him a week or so to find his family. This last episode made it pretty clear that the baby is Shane's. So really it can't have been but 9 months or so. Plus it's been made pretty clear that this was their first winter. They even talked about it at the farm, hoping the first winter would kill off some zombies.
I know a thing of two about big thumbs/small screen lol.