Blood tests and week counting

I went for my blood test on Wednesday 30 September. Went for the results on Thursday, but not all of them had come in. Went back this morning only to find out that not all the required test had been requested, so I had to do another blood test and now waiting until next week to get all the results.

I did get the hcg count though, which says I'm 4-5 weeks pregnant. I doubt that, I reckon I'm more like six weeks. I am estimating due date to 20th May, but will wait until the 12 week scan to get a proper dating.