"Returning to that page might cause any action you took to be repeated" - Django

I have a form on my website, that creates an entry in database. So every time when I refresh a page I got this message first:

The page that you're looking for used information that you entered.
Returning to that page might cause any action you took to be repeated.
Do you want to continue?

Obviously I don't want have the same information more than once in my database.

just in case: this is my code (I know there is a lot of crap that needs to be deleted):

#views.py
@login_required
def subject(request,username, subject_name):
    subject_id = Subjects.objects.filter(user = request.user).get(name=subject_name)
    #Upload form
    if request.method == "POST":
        if "upload-b" in request.POST:
            form = ContentForm(request.POST, request.FILES, instance=subject_id)       
            if form.is_valid(): # need to add some clean functions
                 up_f = FileDescription.objects.get_or_create(subject=subject_id,
                                                  subject_name=subject_name,
                                                  file_type=request.POST['file_type'],
                                                  file_uploaded_by = username,
                                                  file_name=request.POST['file_name'],
                                                  file_description=request.POST['file_description'],
                                                  image = request.FILES['image'],
                                                  )
form = ContentForm()

#Show uploaded files with respect to clicked session (Homework, Class , Random ... )
homework_files = Homework.homework.filter(subject_name__exact=subject_name,
                                         file_uploaded_by__exact=username)
class_files = ClassPapers.classpapers.filter(subject_name__exact=subject_name)
random_files = RandomPapers.randompapers.filter(subject_name__exact=subject_name,
                                           file_uploaded_by__exact=username)




return render_to_response('subject_content.html', {'form':form,
                                                   'subject_name': subject_name,
                                                   'class_files': class_files,
                                                   'homework_files': homework_files,
                                                   'class_files': class_files,
                                                   'random_files': random_files,
                                                   },
                           context_instance=RequestContext(request))


#forms.py:
class ContentForm(forms.ModelForm):
    file_name =forms.CharField(max_length=255, widget=forms.TextInput(attrs={'size':20}))
    file_description = forms.CharField(widget=forms.Textarea(attrs={'rows':4, 'cols':25}))
    class Meta:
        model = FileDescription 
        exclude = ('subject', 'subject_name', 'file_uploaded_by')


#template
    <div id="sbj-creation-frm">
        <h3>Upload File</h3>
        <form action="." method="post" enctype="multipart/form-data">{% csrf_token %}
            {{ form.as_p }}
            <input type="submit" value="submit" name="upload-b" class="btn-create" />
        </form>
    </div>