What is happening?

Brooke • My name is Brooke I`m from Wisconsin. I like fishing and hanging with friends!:)
So my period was 2 days late I didn't think anything of it. It was light the first couple days, usually it's heavy or medium. It's my 3rd day and it's not even there. Usually my period lasts 5 days. I'm on birth control, have been for awhile now and had sex Friday but we used a condom. Why is my period so different this month?