Im on birth control and i had unprotected sex on cycle days 16 and 26 (placebo week) and took plan b both days and now im 5 days late and took a test and came out negative, should i be concerned?

Can do preg. test: Plan B can alter the menstrual bleeding for the cycle in which Plan B was taken, and sometimes the next cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, because Plan B works most of the time, but not all the time. If using birth control pills properly every day, after the first month, a woman has no fertile days while on the pills.