Girls, help, maybe someone had something like this. Week 22. Already t…

Girls, help, maybe someone had something like this. Week 22. Already the second time I notice in discharge a thick brown dot. Small, about 2 millimeters. Yesterday it was once, then in subsequent discharges I didn't notice. And here today again saw it in the evening. It doesn't smell of blood, there is no smell at all. What could it be? Is it dangerous? What should I do? Ultrasound of the cervix?