Hi and

!
When you take yourself off of a BC pill, you're removing a hormone from your body that tells your body when to have a period. Like, when you take your placebo pills to start your period, the lack of hormone in those pills is what tells your body it's time to have a period. Same with if you just stop taking it, your body will think it's time for a period, so that's pretty normal.
However, if your cycle don't return to normal soon, you might want to contact your doctor.
Good luck!