OperationalError occurred while adding new fields in Django

Question

I have a web app I've been managing for months, and I attempted to make some updates on my app. I added new fields to the existing class, but django raised an error.

These are what I've done.

1. Added a new field to an existing model.

class ExistingModel(models.Model):
    # Existing Fields
    new_field = models.IntegerField()

2. Attempted to make migration

$ python manage.py makemigrations

However, it raised django.db.utils.OperationalError: no such column during this process.

• I added django.contrib.sites to INSTALLED_APPS in settings.py.
• My django version is 2.0.3.

How can I add new fields to the existing model?