Miscarriage??

Victoria

Guys i am very confused and a bit sad. I started new birth control pills last month. Everything has been fine my boobs got a bit bigger, i have been having heat waves, and a bit of spotting(which they said is normal for this birth control) yesterday i was supposed to start my period. Everything was normal same pain, bleeding and everything. And then i thought i was passing my normal clots and i go in the bathroom and i passed this. I have i have never passed anything like this. I went to the ER and they said i wasnt pregnant or had a miscarriage. But i havent bled since and i have cramping on my right side that i dont normally have. Someone please help. What can this be? Miscarriage? Something else?