Getting 'relationship does not exist' error while migrating singelton model

[Nadir-Alishly]

I was using sqlite3 for my database, and then I switched to postgres database, then I deleted all my migrations to start from clean sheet. Now when I run command python manage.py makemigrations I get

...
...
...
django.db.utils.ProgrammingError: relation "scholarship_scholarshipconfiguration" does not exist
LINE 1: ...larship_scholarshipconfiguration"."deadline" FROM "scholarsh...

here is my model:

from django.db import models
from solo.models import SingletonModel

class ScholarshipConfiguration(SingletonModel):
    is_active = models.BooleanField(default=False)
    application_template = models.FileField(upload_to='scholarship_templates/')
    deadline = models.DateField()

class ScholarshipApplication(models.Model):
    first_name = models.CharField(max_length=100, null=False, blank=False)
    last_name = models.CharField(max_length=100, null=False, blank=False)
    application = models.FileField(upload_to='scholarship_applications/', null=False, blank=False)

    class Meta:
        verbose_name = 'Scholarship Application'
        verbose_name_plural = 'Scholarship Applications'

and my database setups for sqlite3 and postgres:

sqlite

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': BASE_DIR / 'db.sqlite3',
    }
}

postgres

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': '<dbname>',
        'USER': '<user>',
        'PASSWORD': os.environ.get('DB_PASSWORD', ''),
        'HOST': 'localhost',
        'PORT': '',
    }
}

After getting error I switched back to sqlite3 and made sure that it works on sqlite3