Probably stupid

So this might be a stupid question but I'm new to taking the pill and how it works with my body. I started taking the a week ago so I'm currently on week 2 of the pills, but it's my first pack and I took plan b before starting. Since I'm taking the birth control, I won't get me period until week four right? I know that plan b messes with your period but I don't know if it still will since I'm on the pill now. This app says I should be getting my period this week even though I just had one two weeks ago, so I'm mostly just confused.