Miscarriage?

My period was about 2 weeks late which is weird because my cycles are always pretty regular. Me and my boyfriend weren’t using protection so I took a pregnancy test a few days after it was late and it came back negative so I was waiting to take another one. Then yesterday I woke up with bad cramps and when I took my tampon out this was on it? It is like a large chunk of muscle tissue. The rest of my blood is all dark brown. I’m not sure what to think of all this, if it was a miscarriage or if something else could be wrong with me. Has anyone had any similar situations or know what could be going on?