Help.

I am currently on the pill. And next week is supposed to be the week I start my period. But Wednesday I went to sixflags and i started bleeding that day.

That came out of me yesterday. But this morning another sac like thing came out but it was bright red. What is happening.?? Also a week before I started taking the pill I had sex with my boyfriend. And i bleed a huge amount during it and that was the first time I saw a bloody sac come out of me. Is it a blood clot?