Tams - I'm getting that pain as well, it's horrible when I have to chase after a toddler all day, but I'm pretty sure that for me it's from a pinched nerve, possibly even sciatic pain, as I had a similar thing with DS, though not this early in the pregnancy lol
I was in agony yesterday, and we've only got panadol in the house so I had to keep dosing up on that every 4 hours just to be able to move from the lounge room to the kitchen and toilet and back again when I needed something.

I hope your pain goes away soon!