Meg--
Popping in from the December DDC. I had a lot of this a few weeks ago, right around 4 weeks.. I think mine was maybe a little lower than what you describe, and always on the left side, but sounds similar- sort of a deep, stabbing pain, not really cramps. I convinced myself that it was the little blob burrowing in deeper, but who knows. It would come and go over the course of several days. I'm now almost 7 weeks, and as far as I know, everything is okay.
Hang in there-- I'm learning that the first trimester is just really unsettling.