Add a column to heroku postgres database
Did you run schemamigration before? If yes, go to your database and take a look at your table  "south_migrationhistory" there you can see what happened.
If you already did the steps above you should try to open your migration file and take a look as well, there you can find if the creation column is specified or not!
So, locally I've changed my models a few times and used South to get everything working.  I have a postgres database to power my live site, and one model keeps triggering a column mainsite_message.spam does not exist error.  But when I run heroku run python manage.py migrate mainsite from the terminal, I get Nothing to migrate.  All my migrations have been pushed.