South migration in django

Question

I added a new field in an existing model in django. Note that this app is already converted to south. To apply my new changes I ran these commands

   python manage.py schemamigration my_app --auto
   python manage.py migrate my_app

This is giving an error like "Table 'database.south_migrationhistory' doesn't exist".

So I try to migrate south.

   python manage.py syncdb
   python manage.py migrate south

But this results in the same error "Table 'database.south_migrationhistory' doesn't exist".

How do I solve this?