Facebook not pulling images from post

When I share my post on Facebook, it does not pull my image from the post (either featured image or any other images). Instead it chooses my header image. I don’t know why I am having this problem now – I didn’t have this problem last week. I was able to share my post and have the right image show up on Facebook. I don’t think I have changed anything on my site since then (other than adding new content). I believe my plugins etc are all the same. Can anyone help me? Thanks in advance.