Django Heroku Postgres - ProgrammingError: relation does not exist

I'm using Django 1.7, PostgresApp (PostgreSQL 9.4), Python 2.7.

I have followed this tutorial for setting up and creating the app: https://docs.djangoproject.com/en/1.9/intro/tutorial02/

In the Python shell, I kept getting errors like "ProgrammingError: relation "app_table" does not exist" for my database schema.

So I used the classes from the tutorial:

class Question(models.Model):
  question_text = models.CharField(max_length=200)
  pub_date = models.DateTimeField('date published')


class Choice(models.Model):
  question = models.ForeignKey(Question, on_delete=models.CASCADE)
  choice_text = models.CharField(max_length=200)
  votes = models.IntegerField(default=0)

and then in the shell I got (the correct values):

>>> Question.objects.all()
[]
>>> Choice.objects.all()
[]

Then, modifying the name Choice to MyChoice gives this:

>>> Question.objects.all()
[]
>>> MyChoice.objects.all()
...
ProgrammingError: relation "app_mychoice" does not exist.

Why is this happening? I tried the answers suggested in other posts

./manage.py makemigrations; 
./manage.py migrate auth; 
./manage.py migrate and 
python manage.py syncdb

but nothing worked.