I have some absolutely awesome news!
After festering in misery overnight, and far too much sleeplessness than was necessary, I decided to ring the EPAU where I am booked again.
I explained my concerns, and that I knew my dates exactly. They offered to see me, to do bloods, and see if my HCG rises normally in the next few days. I gratefully accepted this and made my way up this morning. They told me they had no Doctor, so it would just be a case of doing bloods and then on my way.
It turns out, when I got there that they decided to scan me again, to check the measurements as they agreed there was no way a positive test on 24th Feb should be giving measurements of 5 weeks.
Turns out, WE HAVE A HEARTBEAT!!! I saw it!!! Baby is measuring spot on for 6 weeks today!!!!!!! 
I'm still in shock. I have a little picture too! How utterly amazing that less than 24 hours has made such a difference!!!
PR and Jen I hope you get similar news ASAP!
Feel annoyed at my colleagues now, for such unnecessary worry! Hmpf.