Shan, waiting for another scan is terrible - the longest wait ever! If you had bloods last Friday, ring your doctor and ask whether you can have some more done today (and get a rush on the results!). If the pregnancy is not viable, you should see a decrease in your HCG, but if it is viable and was just too soon for a fetal pole to be seen your HCG will have risen. It will give you a pretty good indicator of whether the pregnancy will progress.

If you were only measuring 5 weeks, I would be inclined to wait at least a week and a half before another scan - 6 weeks is still very early to see anything.