Pregnant soon after miscarriage

Hanna

Looking for advice.. I miscarried on 21st December. Took a pregnancy test a couple of weeks after and it was negative meaning miscarriage was complete. Had unprotected sex a couple of days later. Took a test this morning which was positive. Can I get pregnant that quickly? Even though I didn’t have a period following the miscarriage. Any help or advice would be amazing, anxious!!!