Hiya, please don't worry!
Our boy was fast asleep at his 12 week scan, didn't move a muscle the whole time - apart from his little heart going!

Sonographer had me rolling around on the bed, jumping up and down and all sorts but he wouldn't wake up. She told me not to worry at the time, he must just be really comfy - although i couldn't help myself and did worry until i felt him move at about 18 weeks - i think it's only natural to.
I'm now 23 weeks and he's a right wriggly thing! My 12 week scan was in the morning, and now i can feel him moving i've discovered he does like his lie-ins (like mummy!) as he doesn't really start kicking until the afternoon.
xxx