Why don't all my texts appear when I scroll through my conversations?

I have a Samsung galaxy j7. Forgive me if this is a dumb question but I'm clueless with electronics. If I'm scrolling through a long conversation, I can only see some texts and photos, not all of them. Only portions of the conversations and attached photos will show. Is my phone auto deleting them or something?

It might. In the messages app tap the menu button and go to Settings. There go to 'More Settings' and find the 'Delete old messages' toggle. If it's on, then the phone is purging the oldest messages.