Kinda Personal But Whats Wrong?

Okay this is a little wierd to talk about, but I have kinda a personal question. I'm on birth control and my pills are white and pink, last week or so my pieriod was due and I usually get it 2 or 3 days after I start taking my pink pills, but this time I got it 2 or 3 days before I even start takking the placebo pills. So I'm wondering if that's normal if I'm under a lot of stress, or if I should be worried.