index.php no longer working in permalinks

Using the following structure:

https://www.collegiateacademy.com/index.php/%postname%/

no longer works on my website, though it had worked fine for the past year. The only thing that words now is the default structure:

https://www.collegiateacademy.com/?post_id=n

I know that I need the index.php because my server does not allow me to use mod_rewrite. But why would the index.php thing no longer work?

I do have everything set correctly in the Dashboard > Options > Permalinks.

Thanks…