I Think I Had An Early Miscarriage. My Period Was

I think I Had an early miscarriage. My period was 6 days late but I never got a positive pregnancy test. I started to have really bad cramps and I had heavy bleeding two days ago. The bleeding has slowed down. Now it’s a brown color. I also have a tight feeling in my stomach. I went to medexpress today and they didn’t do anything. They told me I could have had a miscarriage but there is no way to test. Do you have any clue to what could be wrong ? I am going to make an appointment with a gynecologist this week and start birth control.