6 weeks pregnant and very confused, and worried, help!?

I am 6 weeks and 5 days pregnant, and noticed some light brown spotting, and slight cramping which turned to pinky colour, then back brown again, went for a scan, nothing found on u/s, but found a small black circle on internal. The lady couldnt tell if everything was alright as it was so small, only the size of approx 3 weeks, which doesnt make sense to me, as I am sure of my dates. I had a blood test, and have to have another in 48 hours, so bit worried as to whats going on and i have another 24 hours to wait for my next blood test, anyone else come across this? they also retested me I was still pregnant, and I still have pregnancy symptoms, tiredness, extremely sore etc. I'm preparing myself for the worst, and thinking if its so small it must have failed, but have not had any more spotting or cramps since i went for scan yesterday. please help feeling really upset.