I had unprotected sex on the last day of my period. i took a plan b within 12 hours but my period didnt stop. it was very light for about 5-7 days. i have also been under a ton of stress. my cycles range from 24-29 days in length. am i pregnant?

Although "Plan B" is not 100% protective against pregnancy, it would be unusual for pregnancy to occur from "unprotected sex" on the "last day" of what apparently are regular periods noted in your question. The "very light" bleeding for "5-7 days" is probably due to withdrawal bleeding from Plan B. See your GYN physician, and/or obtain a serum HCG test to be certain about pregnancy.