Was i pregnant before?

Hi guys, im currently 7w4d pregnant.

On november, before my pregnancy, i had some irregularities with my period (which was weird cuz it was always regular) and I went to a doctor.

She did an ultrasound scan and said she saw the sac and a tiny little baby. She wanted me to get a blood test for hcg levels to be sure, and my levels showed negative.

She didn’t understand what it was and couldn’t explain and told me that i’d get my period in a couple of weeks.

At the end of december i got pregnant (thank you god 🙏🏻) but i’m still confused about this incident.

Here is the ultrasound scan: