I had a miscarriage 8/9/17

On Thursday I took a pregnancy test and it was negative I have not had a period since mc.

On Saturday and today I have had dark positive pregnancy test.

On the Thursday were I tested negative I had an ultrasound to make sure I had nothing of precious pregnancy due to my tummy still being bloated they told me i ovulated on my left and could see some cells but they never mentioned pregnancy?

So wondering has this happened to you before and or what does it mean?

I am having hcg blood taken out tomorrow.