Anyone know about a bloody sac being vaginally discarged?

Ive had my period this week and when i was in the bathroom I, had this half dollar sized, dark bloody sac come out.

Ive never had this happen before and I have no idea what it is. Im having my period and im not supposed to be, because I take the nuva ring & I keep it in a fourth week so i wont have a period. If anyone cares to wonder why i do this Its because Im bipolar & my episodes are more severe when i menstruate.

Also I have to go see a doctor Friday because they said I needed furthur evaluation after i had my PAP last month. Like I said i dont know what it was and i'd like to have some ideas of what it is so I can tell the Doctor.

Thanks!