"pytest --doctests-modules" AlreadyRegistered error

I am using doctests via pytest with the command "pytest --doctest-modules".  Unfortunately, I keep getting the following error.  I've already attached a screenshot.  Does anyone understand what's causing and how to address it?  Thanks!

============================================== ERRORS ===============================================

__________________________________ ERROR collecting main/admin.py ___________________________________

main\admin.py:25: in <module>

    admin.site.register(PoolType, PoolTypeAdmin)

..\..\..\.virtualenvs\mysite\lib\site-packages\django\contrib\admin\sites.py:109: in register

    raise AlreadyRegistered('The model %s is already registered' % model.__name__)

E   django.contrib.admin.sites.AlreadyRegistered: The model PoolType is already registered

__________________________________ ERROR collecting main/models.py __________________________________

main\models.py:36: in <module>

    class PoolType(models.Model):

..\..\..\.virtualenvs\mysite\lib\site-packages\django\db\models\base.py:111: in __new__

    "INSTALLED_APPS." % (module, name)

E   RuntimeError: Model class mysite.main.models.PoolType doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS.

====================================== short test summary info ======================================

ERROR main/admin.py - django.contrib.admin.sites.AlreadyRegistered: The model PoolType is already r...

ERROR main/models.py - RuntimeError: Model class mysite.main.models.PoolType doesn't declare an ...

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 2 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

========================================= 2 errors in 0.62s =========================================

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