Apple,

If by your dates, you are 4w, then provided that your cycles are regular, it is quite likely that a foetal pole would not have been detected yet.

I would suggest that you talk to your GP again and let them know that you are concerned and ask if you could have another u/s to check on the progress of things, but to me, it sounds all normal based on how many weeks you think you are (i.e. 4, not 5!)