What Could Be The White Sack Like Discharge From Vagina?

A white sack about 3 inches big just came out of my vagina. Im on birth control and sexually active. This is the first time ive had my period since starting my birth control. I missed a few days and me and my boyfriend had sex during those days but then i took the pills i missed 3 days later. Could it have been a small miscarriage? If not then what was it?