Revert yesterday’s changes. Add PFLogin and PFSignup view controllers (not yet subclasses). Remove all confusing segues and stuff.
Subclass Login and Signup views. Eliminate logo and dismiss button on login but otherwise make few changes.
Multiple changes to app. Now users can enter a pain score which is saved to parse with user info. App queries parse to display most recent pain score.

May want to consider undoing the subclass work on PCASignUpController to do it manually, since you want more than one additional field.