Pregnancy after miscarriage?

Has anybody ever been pregnant right after a miscarriage? The day I was supposed to get my period back after the miscarriage I took a test just in case and it was the BRIGHTEST positive test I’ve ever gotten. It’s miscarriage was followed down to 0 hgc so it’s definitely not that pregnancy. My doctor said that it was “a significantly positive test for estimated 5 weeks” and then seen how bloated I was and said she wants a dating ultrasound. Is it normal for the hgc to be so high so early? Could it be twins? Anybody have any experience with this??