What are these??

So today I started my period. Late because of my birth control so I put a tampon in at work and ive been having cramps here and there for a few days now but today they were horrible. Like I could barely stand up so after like 2 hours of stabbing cramps I took the tampon out before going home. When I went to go to the bathroom before bed these came out and ive never had sex. They felt gross like skin in a way. At first I thought they were blood clots but idk..what they are