Took 2 plan b pills with short time in between, now no period for a whole month is this normal? pregnancy test negative.

Sounds ok: Plan B can alter the menstrual 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 (that's about 21 days after sex), because Plan B works most of the time, but not all the time. A urine test done less than 2 weeks after sex might give a false negative result due to testing too early.