herokuでdjangoのpostgreSQLが使えない

Question

現在heroku上にdeployしたdjangoアプリのDBをPostgreSQLに変更しようとしています。

やったことは、この記事を参考に

setting fileを以下のように変え、

"""
Django settings for personal_portfolio project.

Generated by 'django-admin startproject' using Django 2.1.4.

For more information on this file, see
https://docs.djangoproject.com/en/2.1/topics/settings/

For the full list of settings and their values, see
https://docs.djangoproject.com/en/2.1/ref/settings/
"""

import os
import django_heroku


# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))

MEDIA_URL = '/media/'
MEDIA_ROOT = os.path.join(BASE_DIR, 'media')
# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/2.1/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
SECRET_KEY = "省略"

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = True

ALLOWED_HOSTS = ['*']


# Application definition

INSTALLED_APPS = [
    "django.contrib.admin",
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
    "django.contrib.messages",
    "django.contrib.staticfiles",
    "blog",
]

MIDDLEWARE = [
    "django.middleware.security.SecurityMiddleware",
    "django.contrib.sessions.middleware.SessionMiddleware",
    "django.middleware.common.CommonMiddleware",
    "django.middleware.csrf.CsrfViewMiddleware",
    "django.contrib.auth.middleware.AuthenticationMiddleware",
    "django.contrib.messages.middleware.MessageMiddleware",
    "django.middleware.clickjacking.XFrameOptionsMiddleware",
]

ROOT_URLCONF = "personal_portfolio.urls"

TEMPLATES = [
    {
        "BACKEND": "django.template.backends.django.DjangoTemplates",
        "DIRS": ["personal_portfolio/templates/"],
        "APP_DIRS": True,
        "OPTIONS": {
            "context_processors": [
                "django.template.context_processors.debug",
                "django.template.context_processors.request",
                "django.contrib.auth.context_processors.auth",
                "django.contrib.messages.context_processors.messages",
            ]
        },
    }
]

WSGI_APPLICATION = "personal_portfolio.wsgi.application"


# Database
# https://docs.djangoproject.com/en/2.1/ref/settings/#databases

from socket import gethostname
hostname = gethostname()



import dj_database_url
db_from_env = dj_database_url.config()
DATABASES = {
    'default': dj_database_url.config()
}
ALLOWED_HOSTS = ['*']



# Password validation
# https://docs.djangoproject.com/en/2.1/ref/settings/#auth-password-validators

AUTH_PASSWORD_VALIDATORS = [
    {
        "NAME": "django.contrib.auth.password_validation"
        + ".UserAttributeSimilarityValidator"
    },
    {
        "NAME": "django.contrib.auth.password_validation"
        + ".MinimumLengthValidator"
    },
    {
        "NAME": "django.contrib.auth.password_validation"
        + ".CommonPasswordValidator"
    },
    {
        "NAME": "django.contrib.auth.password_validation"
        + ".NumericPasswordValidator"
    },
]


# Internationalization
# https://docs.djangoproject.com/en/2.1/topics/i18n/

LANGUAGE_CODE = "en-us"

TIME_ZONE = "UTC"

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/2.1/howto/static-files/

STATIC_ROOT = os.path.join(BASE_DIR, 'staticfiles')
STATIC_URL = '/static/' # localでcssを読み込むためのパス(たぶん)
STATICFILES_DIRS = (
    os.path.join(BASE_DIR, 'static'),
)

django_heroku.settings(locals())


try:
    from .local_settings import *
except ImportError:
    pass

if not DEBUG:
    SECRET_KEY = os.environ['SECRET_KEY'] # 追加
    import django_heroku
    django_heroku.settings(locals())

下記のステップでdeployしています。

git add -A
git commit -m "Change"
git push heroku master
heroku ps:scale web=1
heroku run python manage.py migrate
heroku open

しかしherokuにデプロイ後に、ローカル環境でアプリのhtmlやcssを変えてして上記ステップを踏んでサイトを更新すると、デプロイしたアプリで更新したデータが消えて、全てローカルのものと同じになってしまいました。

どうやらpostgresqlとsqliteの切り替えが上手くいっていないようですが、色々調べてみたり、他のサイトを参考にsettingを書き換えてみましたが同じで、原因がわかりません。

もしおわかりであれば、ご教示頂けると大変助かります。
何卒宜しくお願い致します。