How Long?

Hey so my bf is at basic training for the army right now... we’ve had sex before but we were risky with the pull out method and rarely condoms... I want to get on BC before he comes back and I know that it takes 3weeks-month for the BC to really work... What I would like to know is that if I go to the doc... how long is it before I get BC? Will the doc prescribe it right then and there after a convo about different options or will I have to do a follow up appointment before I get BC?