SQL Database Operational Error - no such table : users - postgresql

Question

sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: users
[SQL: SELECT users.id AS users_id, users.username AS users_username, users.password AS users_password
FROM users
WHERE users.username = ?]
the above is the error im getting.
class User(db.Model):
__tablename__ = "users"
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(24), unique=True, nullable=False)
password = db.Column(db.String(), nullable=False)
this is my User code.
#app.route('/', methods=['GET', 'POST'])
def index():
reg_form = Registeration()
if reg_form.validate_on_submit():
username = reg_form.username.data
password = reg_form.password.data
# for checking if someone has taken the username already
user_object = User.query.filter_by(username=username).all()
if user_object:
return "This username has been taken. Try another one.."
#registering in the database and commiting and etc
user = User(username=username, password=password)
db.session.add(user)
db.session.commit()
return 'Registered into the database!'
return db.create_all()
the application code.
I'm unable to figure out.. any help would be greatly appreciated. Btw im trying to make a registration system where the username and the pass get stored in Postgres Database.