I save every chat message I get from a person I speak to, but when I scroll back I can only go back so far before it stops showing me the messages. Why is this?
Snapchat is developed to delete messages once they are seen. This has been the whole idea of the application in the first place. The app will show you messages for the current session or for a limited amount of time, but after that, everything gets deleted. You can't have an entire history for conversations. Install and use WhatsApp or any other related app if you want to keep a history of your chats.
Download WhatsApp: https://www.whatsapp.com/