Thank you for posting your question here, I will try to answer it to the best of my abilities.
If you have taken all the pills regularly and on time you shouldnt get pregnant during placebo week. Another thing worth remembering is that usually the period kicks in during the 4-5th day of placebo week.
Some women have found that when they start taking the pills for the first time in their lives, they dont get their periods till the 3rd month of using them, so if you are using them for the first time that may very well be the reason.
I know all this is probably not as helpful as you want it to be so I recommend you take a home pregnancy
test, that way you can be sure and relax.
I hope this answered your question.