Add infinite scroll to thumbnails

I’m using a related post plugin on all my posts/pages that displays a thumbnail, title, description, and link for all my post.
Trouble is, I have 175 post so I’m having to load 175 thumbnails and growing.

I would like to add infinite scroll but I’m not trying to scroll the archive pages I would like to scroll the plugin content.
Here is a screenshot.

I would like to load about 3 rows of 6 and then infinite scroll through the other 150 or so.

How could I do this from scratch? As I don’t think another plugin would do the trick.
Or would it?

Thanks.

The page I need help with: [log in to see the link]