Instagram post captions matching with your target keywords can be analyzed easily
If you have a Facebook developer account, you can integrate your app with Pivony so that it can collect and analyze the posts of the last 7 days. When you set it dynamic, it will keep fetching the new posts and consolidate in your dashboard.
Note that it's allowed to fetch the captions only. Facebook does not let you fetch the comments of Instagram posts unless the post is submitted from your Instagram account.