Simple WordPress question.

Here's the current layout:



I have two pages on one website. Both have the layout as the one in the image above.

Category 1-3 are sub categories (children?). One main category is listed as id 1, while the other as id 2.

When a person visits one of these two pages, they see all the posts from Categories 1-3, with pagination at the bottom, so that it won't end up being one long page. When a person clicks on the post on the left, it loads just that post.

The issue I'm having: When a person clicks on Category 1, 2 or 3, it displays the posts belonging only to that category (which is correct), but not the table of contents on the left. I can't figure out which file I have to edit (or add) in order to get the table of contents to display once that category's posts load up. Problem is that on one page style I have cat id 1, while on the other I have cat id 2, so I don't think I can cover both pages (which contain these layouts) with just one file.

Can anyone suggest some kind of a solution for this?