Force 'www.' in all path names

What can I do to force a preceding ‘www.’ before all URL path names used in WordPress? My resources cannot be located with out it.

For example, right now all my styles are being referred to by “https://mydomain.org/path/to/styles/style.css,” but I need it to say, “https://www.mydomain.org/path/to/styles/style.css”

Is there a setting I can change to fix this? I cannot log in without this functionality.

Thanks!