If i'm on doxycycline hyclate can i take plan b and will plan b work?

Not at the same time: Tetracycline tends to combine (chelate) with most hormone products rendering them less effective. If you need to use Plan B you must not have used Tetracycline for at least 8 hours prior to allow Plan B to be absorbed. Plan B, under ideal circumstances still has a "failure rate".

Yes: Plan B is a progestin, Doxycycline interferes with estrogen absorption, so the combination theoretically should be okay