I don't normally take birth control. but i had unprotected sex and was told if i take 3 birth control pills it works like plan b? is this true? how?

Not exactly: Some pills are designed to be emergency contraception pills (those work best). Regular birth control pills have various hormones in them, and SOME types of those pills can be taken to try to prevent a pregnancy. One can also get an IUD, which works well as emergency contraception (ask one's Ob-Gyn doctor). A reference table can be found at: http://ec.princeton.edu/questions/dose.html#dose