TMI- possible miscarriage?

Sarah • 19. |T.R.F. 1.29.16💘| IT ‘19 💚 BSU ‘22 ❤️
WARNING- THE PICTURE IS GROSS. IF YOU DO NOT HAVE A STRONG STOMACH, DO NOT LOOK AT THIS POST. I know it'll put a TMI warning but it's literally a picture of a huge blood clot. I warned you.
So I didn't have a regular period since March. I missed it April and May and spotted in June so I took pregnancy tests and out of 3, 1 came back positive. Since 2 others were negative I disregarded it and carried on with my life thinking it was my birth control (I'm on nexplanon). So, this month, I finally got a regular period. Well, I went to the bathroom and found this when I wiped. 
I don't know if it was a miscarriage, or if I'm having cysts, but while I was thinking I possibly could be pregnant I was having some symptoms such as growing breasts and constant nausea. I thought the boobs thing was just me growing, so once again disregarded it. I also hadn't been eating well AT ALL so disregarded the nausea as well. Does anyone have any idea what's happening to me? It's freaking both me and my boyfriend out.