I Started On My Period Lastnight This Morning I Was

I started on my period lastnight this morning I was experiencing very severe abdominal cramps I later went to the bathroom and felt something was gonna come out eventually it did, it was maybe 1 inch long and it look very clear and bloody at the same time shaped as a ghost figure best I can describe. Now my cramps feel normal than before. What could of it been? ( I am taking birth control pills)