We had the dating scan today, and I'm pleased to announce that all is well. Good healthy heart beat, and baby was even performing a little dance for us (mainly 'reaching for the lasers').
It's a big relief to know that everything is well. With my current mood I had convinced myself that something was wrong with the baby. I still feel a bit detached, but even as I write this a few days later things have improved and I feel more positive which is good.
So the 'official' due date is: 29th May 2015.
It seems a long way away, but I know how quickly it will go!