Strong positive urine and negative blood

A bit of background: 43, partner is 53, we had our little bundle of joy in December 2019 with a single round of <a href="https://glowing.com/glow-fertility-program">IVF</a> after trying for 2 years and 1 chemical pregnancy at 5 weeks.

Now, I had my first period after giving birth on Dec 15 2020 not too worried in taking precautions, but no period yet, took an expired pregnancy test at home on Jan 28 and bang strong positive. Ok maybe because it was expired. Went to get a new pack, tested the same day and again strong positive. Went then straight to the doctors for blood and today I got the call the results are negative. Doctor said hcg was 1, so definitely negative.

I tested then again today and still strong positive and no sign of AF.

What’s going on??

First top it’s the expired one, then Thursday and today (Saturday) test 🤷🏻‍♀️

I had full blood screen in November, no signs of UTI either