Loading shortcode after other code

I have written some shortcode that pulls the ID from each heading and displays it in a table of contents for that particular page. It currently grabs all IDs that already exist on the headings.

I have also written some code that dynamically adds IDs to all headings if they don’t already have them. The shortcode does not pick up on these IDs.

I think it is because the shortcode loads in before the ID generating code runs. How do I change the load order of all of these pieces of code?