You are protected all day every day equally as long as you take one pill every day. You are just as protected during your placebo week as any other day of the month. A problem only arises if you extend your placebo week past 7 days; then hormone levels can drop very low, causing you to ovulate and possibly conceive.
You really had no need to take Plan B.
But don't freak out if you don't get your period or your cycle is a little weird! Plan B is a very large amount of hormones in one pill, and it can cause your cycle to get very thrown off. You may have a period when you're not supposed to, you may have breakthrough bleeding for a while, and you may even not get your period when you are supposed to. NONE of these things mean you are pregnant! It just means your cycle needs time to get back to normal, in fact, as many as 3 months to resume its regular course.
Plan B is very effective; and since you are also taking OCs, your chance of pregnancy is so very very very slim. In my opinion, there is little to no chance you are pregnant.
If you want, you can take a test and get an accurate result 17-18 days after sex. Good luck, but I'm sure you'll be fine.
