I'm on birth control I also take doxycycline which makes it less effective so I used a codom and it broke so I took plan b can I still get pregnant?

Unlikely. Unlikely but possible. Do a pregnancy test if the end of the cycle shows no period before you start your next pack of pills.
Unlikely. Plan B One-Step is up to 89 % effective when taken within 72 hours (3 days) after unprotected sex. It can reduce chance of pregnancy by up to 95% if used within 24 hours. .