Progesterone and brown spotting during pregnancy

I had 2 chemical pregnancies last year ( before they diagnosed my thyroid problems- hypothyroidism), they controlled my tsh levels with Synthroid. After that, we conceived with the 4 round of <a href="https://glowing.com/glow-fertility-program">IUI</a>, and I was put in progesterone ( intravaginal ) as a preventive measure. I started with a bleeding in the 5 week, the bleeding is not much and very dark brown. I continue to test and I still get dark lines in the pregnancy tests.I spoke with my fertility clinic over the phone about it and they told me that it could be the progesterone that I am using, that’s why the colour is so dark and I need to wait until my upcoming ultrasound that will be in a week and a half. I am just wondering if there’s someone else that went through the same. And what was the outcome. Will appreciate any info, thank you.