Austin asks the Noobs for their crackpot theories on Amy’s pregnancy… or lack thereof. Why can’t the TARDIS decide if she is or isn’t?

To boil down Corbin and Tripp’s answers, it’s wibbly wobbly, timey wimey… stuff. They believe that there is some part of the timeline that is still in flux. Once it settles out, then the TARDIS will be able to get an accurate reading on Amy’s belly!