I want to know if it's possible to add more photos to a post that got created by sharing a single photo. I can't find a way.
In contrast, when I share a couple (or more) photos in a post, a kind of pseudo-album is created. I can always go back later and add photos to this pseudo-album, and (after a small while) the new content gets reflected on the post.
Best Answer
From the lightbox view select "photos from posts" that should take you to an album view where you can add photos.