I had unprotected sex 3 days in a row (he came in me each time, twice in one day), on the 3rd day i had peak ovulation (confirmed by test) and also took a plan b. is the plan b effective then or is it too late?

No guarantees: 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. There are no guarantees in life except for "death and taxes." If worrying too much about it, one can ask her Ob-Gyn today about an IUD.