Top 10. Doctor insights on: Positive Pregnancy Test One Week After Period. 1. Hi, I'm currently on Mirena for 3 1/2 yrs now, my period is stable every 3 to 4 weeks but never late, now I'm almost 3 weeks late with one positive pregnancy test when i was 10 days late and a negative blood test(1.2 beta hcg ), internal ultrasound not sh.