I’m starting to wonder wth is going on with me?

I have had a consistent period since I’ve been off birth control for the past 18 months. I also had a miscarriage a few months ago. 😔 I get it every month on the 19th or 20th. Last month, I didn’t have a period at all. I have taken several tests. They are all negative. And today after I wiped, I had a small amount of dark colored, discharge looking blood. I have made a dr appt for next week. But was wondering if y’all had any ideas what could be going on??