Are you using a custom workspace that takes your second screen into account? If not then you absolutely should do that.
Is Photoshop closing OK by using File Exit or F4 for instance? If Photoshop does not close properly then it will not save its last used settings and will switch back to old settings the next time it is opened.
As a new CC user are you aware that you can save custom keyboard shortcuts with custom workspaces? This is incredibly useful, and especially so if using multiple screens.