Facebook typically scrapes a URL whenever you try to post it in order to gather the information on your page. If you have updated your page since the last time you may have posted it, Facebook may need to re-scrape your page to see the new content. It usually does this on its own, but you can usually trigger it by pasting your link a few times without posting until you see the updated info.
Here is a link to a tool Facebook provides to check your share link content as well:
You can paste your link there and click 'debug', then review what Facebook sees in your post. You can click 'fetch new scrape information' as well to tell Facebook to get new information from your page if it isn't there.