Brown Clot

I'm 12 weeks and had a stain of pink blood when wiping this morning. Now, this evening, I passed a brown clot the size of a nickel. I'm freaking out. For one, I just stopped progesterone supplements 3 days ago - I was told to stop taking it at 12 weeks. And two, I had a painful ultrasound yesterday (the tech pressed really hard for a good 10 minutes during my nuchal scan) but we saw our baby moving around and a strong heartbeat of 164. Was it the ultrasound? The progesterone? Has anyone passed brown blood/clots and been OK?