the brown dicharge was just your period ending, sometimes the blood at the end of your period is "old" blood so it is brown.
and like it was said above just because you dont like the smell of cigarettes dont mean your pregnant.
yes some women have periods while there pregnant, but there not a "normal flow" its usually a lot lighter.
i have been having unprotected sex for months now because im trying for a baby yet im not pregnant yet, so theres a good chance your not pregnant
take a hpt anyway