relation "background_task" does not exist
I don't know if this is still valid question but what helped me was to revert all changes in code related to background_task module and then applying migrations. After that reapply your changes in code and it should all work.
I'm trying to run some tasks in the background while running a django server. To do this, I'm using background-tasks library. I've followed the following steps:

pip install django-background-tasks
Added 'background_task', in INSTALLED_APPS in settings.py 
python manage.py makemigrations background_task

The problem arises in the 3rd step giving an error stating:

django.db.utils.ProgrammingError: relation "background_task" does not
  exist LINE 1: INSERT INTO "background_task" ("task_name",
  "task_params", "...

I've tried looking for other solutions but every one of them was the 3rd line. 
How should I proceed ?