gestational sac measuring 5weeks 3days but a negative hpt??

I'm so confused as to what is going on with me. Had a mc on 2nd Sept I was 5.5weeks. Had a scan 3rd Sept and midwife said all had cleared and uterus was empty. I then took a period 1st Oct which was pretty heavy with clots and all. I went for my 1st fertility app yest and they gave me an internal scan to check ovaries womb ect and she said she can see a gestational sac measuring 5weeks 3days. No yolk sac can be seen but she said that's normal for that far along. could it be something left in me from last Time? Could I be pregnant again but losing it too as negative test? I'm so confused 😣