Gestational sac on transvaginal ultra sound, but negative pregnancy tests

[BitConfused1]

Hello, I had a TV ultrasound on 23 January this year and it showed a gestational sac and the sonographer recommended I'm referred to pregnancy services. However, I had a period on 17 January. Also, I'm about to have another period now (yes, it's a bit soon). Also, the 2 urine pregnancy tests I did were negative and my hCG blood test (done yesterday) is <0.6.

I'm really confused. So is my GP. He's referred me for another ultrasound.

If it's not a gestational sac, what might it be?

I had a CA125 blood test for ovarian cancer and that was negative.

Also, a hCG level of <0.6 seems really low in general.

Hi, I forgot to add that I have never been pregnant and I am not trying for children with my husband. The gestational sac on the ultrasound came completely out of the blue and I am confused.