Being honest - do you think your old company would take you back? I've seen many do it...but not within a week or two of leaving. Usually it's after a year or so.
If you do go back, would the company have you locked? As in, you wouldn't really get any major pay increases from this point forth.
I'd stick it out for a while. The first couple weeks at a new job can be tough on anyone...and most second guess their decision. This does not come from my experience though...as I've been at my job for over 17 years.
