Miscarriage? or just weirdness? Caution possible TMI !!!!?

I am 22, have had regular-ish periods my whole life and have a 2 year old healthy baby boy (no complications with that pregnancy). I was 1 1/2 weeks late on my period and took a pregnancy test last week which turned up negative... then yesterday I started brown spotting (not usual for me) and a large (quarter sized) piece of tissue came out. It was fairly thick as well like 2mm and did not dissolve like a clot ( I picked it up and looked at it to make sure). I feel extremely fatigued and ill ... just drained and my period is now almost non existent to very light and still brown. I know this is disgusting but I am so lost and need help. Serious answers only please! Thanks