Heavy period or early miscarriage? Help!

I need some help/advice if anyone else has experienced this. I normally have an irregular period so when it's late I usually don't think anything of it. Except this time it's been super late. Normally I wouldn't think anything of it but my husband and I started ttc. I did have some cramping a little while ago but no bleeding. All pregnancy tests have been negative. I finally started bleeding on Wednesday but it was pretty heavy for my usual beginning of my period. That night and the next day I experienced the worst cramps of my life. My flow is extremely heavy and has had some dark colored globs (forgive me idk what they are called). I actually bled through my pad (it was 90% soaked) panties and pants which I have never had happen before. It does not seem to be slowing. I write to you all because I'm concerned from what I've read that this may actually be an early miscarriage and not just a heavy period. I am super new to all of this so please any thoughts or advice would be great. Thanks.