I Am Taking Microgestin 1.5/30, And Have Been For A

I am taking Microgestin 1.5/30, and have been for a few years and had unprotected sex for my first time. I usually take my pills on time, one everyday, but sometimes i forget and have to take two that next day. Should I take Plan B while still on my microgestin pills or just rely on the birth control pills? I'm afraid if I take both then my period will come too late? Thank you