I had unprotected sex on august 10th 11th and 12th my period was due the 19th took plan b on the 11th? period hasn't come yet could i be pregnant?

Did you check a UPT?: If you had unprotected sex, then of course you could be pregnant. Plan B, while effective, it shouldn't be your primary birth control method. There is about a 5-10% chance you're pregnant.

Possibly: Having unprotected sex on three consecutive days and taking Plan B in the middle may result in pregnancy. Plan B can also disrupt the menstrual cycle, so you may need to do several pregnancy tests if your period is late to rule out pregnancy.