I hate to hear that you're having some trouble finding your photos and videos. I'll be happy to provide some insight about this.
You mentioned that iCloud has backed up your iPhone before. You can locate iCloud backups by using the steps here and scroll near the bottom where it says "Locate and manage iOS backups stored in iCloud": Locate backups of your iPhone, iPad, and iPod touch
If you had iCloud Photo Library turned on, then your photos may be in iCloud. You can check If you sign in to iCloud Home using a browser on a computer and clicking "Photos".