How Do You Know If You Had A Miscarriage

My question is if your ttc and don’t know you conceived and start bleeding how can you determine if it’s just aunt flow or a M/C ? I thought I would get a bfp this month but then Af came 3 days early & it started with clots ( black gooey, slimy like clots. T.M.I sorry ) I passed clots the first 2 or 3 days I’m On day 4 and really haven’t passed and more & the bleeding is tapering off . I am no longer cramping either. I assumed af was coming but could it have been a m/c. I was having some back pain here and there along with vomiting